First some sources you might want to check out. Volume 2 of the history of sexuality by Michel Foucault is a good start. I honestly can't think of the other secondary sources I've read on it, but the bibliography on the Wikipedia page seems to have some good stuff. For primary sources check out some of the pottery and stuff here and check out some Socratic dialogs (Symposium by Plato might be a good start, it features a young and very drunk man flirting with an older Socrates and calling him a tease).

My take on it (and everything I'm going to say can be contested on his grounds). A) Pederasty was not universal, but mostly only practiced among aristocratic families. B) Most young boys/men who were in the receiving end of a relationship sought out a young lover when they themselves had aged (similar to evidence that many modern pedophiles were themselves victims of abuse). C) Most importantly we cannot attempt to place our own moral judgments on these ancient categories. I know if no evidence to suggest it was causing harm. I know of people arguing vehemently against it, but on the grounds of it being unnatural, not on the grounds of it damaging young men's psyches, and these criticisms came long after the classical Greek period (St. Paul being a good example, especially some passages in 1 Cor).

I won't get into questioning whether we can say PTSD existed before it was labeled, which is admittedly a silly debate. I will say that abuse is to some extent culturally determined. I think a good example is the debates about circumcision that happen on reddit everyday. People have very strong opinions either way. One can see how the "it's abuse" side could develop psychological scars from being circumcised, and how the "it's not abuse" side won't ever care and won't develop problems. It doesn't matter which side is right, what matters is how the individual interprets and values their experience. Nobody that I know of in the classical ancient Greek culture considered the practice to be abusive, so in my way of viewing the world I can't imagine someone developing psychological issues from pederasty alone (maybe if there was some beating or gas lighting or something else added in the outcome would be different), and I think it's intellectually lazy to take our current social values (my long spiel should in no way be read as a justification for contemporary child molesters) and attempt to condemn and long lasting and highly valued ancient institution.

Ancient Greece is kind of outside my area of expertise, but I can give a very general answer. First, you need to understand that a lot of the people you see being referred to as "boys" in Greek sources weren't, strictly speaking, children - a lot of them were likely to be what we could call teenagers or adolescents. Second, it should be noted that these relationships were to some degree consensual: in theory, the younger partner had consented to the relationship and was a willing participant.

Now by our standards, today, we'd recognize that there's a power imbalance there. And in our culture, we tend to be of the opinion that someone that young can't meaningfully consent to a relationship with someone that old, especially when they're far from "equals" in society, and where there's a give-and-take (as there was with pederastic relationships - the younger partner was often well-treated and provided for by the older one). But the Greeks, for the most part, don't seem to have seen it that way, and pederastic relationships were generally considered "normal" by the standards of the time.

So the question of whether or not there was trauma as a result of these relationships is actually kind of hard to answer: are we looking at a consensual, loving relationship? The Greeks certainly talked a lot about and praised the "love" of between a "boy" and man, in fact they often viewed it as superior to the love between men and women (in part because "boys" had to be wooed, while women often had less power, and therefore less choice in the matter). We can certainly envision situations where both partners were happy to be in this relationship, and where they both benefited, and where it was seen as perfectly normal by everyone else. It's hard to imagine how a relationship like that could be the cause of trauma or psychological harm.

But it's also possible that much of that is window dressing - it's possible that as much as the Greeks talked about being in love with and wooing "boys," there was a considerable amount of coercion involved, or that specific relationships were coercive, abusive, and exploitive. So it's also pretty easy to envision a scenario where many of these relationships really were traumatic for the younger partner, in which case we might speculate that they'd suffered physical/psychological harm.

As far as I know/have read, the bottom line seems to be that we just don't really have the evidence to know for sure. Being the younger half of a pederastic relationship wasn't really something that people wrote about, and I'm not aware of anyone who wrote or gave a detailed, first-hand account of what it was actually like to have that experience. We certainly have evidence which suggests that these relationships were normal and not perceived as traumatic. But the devil of these things tends to be in the details, and as always with ancient sources, we're only dealing with a narrow slice of what might have been written/known about these things.

I am reading a book on this topic: Christianity, Social Tolerance, and Homosexuality: Gay People in Western Europe from the Beginning of the Christian Era to the Fourteenth Century by John Boswell. In his introduction, while defining terms, he addresses the implication of the word 'boy' from ancient times to the Middle Ages. Youthfulness is often equal to attractiveness and sexuality. Even today when commenting on an attractive female we will use the term girl "even if she is twenty or more years beyond 'girlhood'". "In modern American culture teenaged girls are ubiquitously standards of feminine beauty. It would certainly be wrong, however, to infer from this that most men either wish to or do have sexual relations with women from this age group." Boswell goes on to cite our use of girlfriend and boyfriend when referring to couples of all ages, even if one or both are much older than a youth. We refer to our significant others with names like sweetie, baby, cutie. We go out with the boys/girls for the night.
Boswell goes on to fully explain the Athenian notions of "an idealized cultural convention" of an older/less attractive/lover and the younger/more attractive/beloved. "It is apparent that the roles were not predetermined, since there was often uncertainty about which person played which part, even when their respective ages were known. The same person, moreover, might be both lover and beloved of different persons at the same time." Christian monks with their "symbolic filial relations" continued the equation of youth and eros: Alcuin writes to a cleric "beautiful boy", Strabo addresses a monk as "little lad". Neither were children.
My amateur take on completing this book is translation/anachronism of ancient erotic literature/poetry was imitated for thousands of years only to be twisted into the intolerant myth of predatory and unnatural homosexuality by late Middle Age Christian moralists. I know this is a major sweeping statement with many nuances that I am failing to mention. I highly recommend this title for more fascinating depth. Also, his book on orphaned children, The Kindness of Strangers.