Many young Romans entered life as an apprentice anywhere from 12-15, depending on what they and their parents wished, and the profession of their father generally (but not always) determined what they apprenticed in. Many males would also volunteer for military service, which you generally had to be over 18 (or close and exceptionally strong), as military service was a pretty solid way to get a plot of land and some wealth if you survived it, and was usually necessary if you wanted to enter the political theater. Usually, though, workplace training began in the beginning of their teenage years, and the poorer you were, the younger you started.

I touch on this topic a bit in this post concerning the "middle class" Lucian. I think it illustrates a fairly applicable principle, namely that children's entrance to the economy was heavily dependent on their family station and personal connections. And while "apprentice" carries worryingly medieval implications for me, it really is the best term.