Saw a comment on an r/AskReddit thread about commonly believed myths and it talked about arrange child marriages only being done by mobility and royalty.

Piggybacking off this, that girls were married off in their early teens in the medieval period. This is based off the nobility and royality, who did marry off their young daughters as a political tool to secure alliances. However, even when the young royals were only 12 or 13 when wed, they were often married by proxy and married "in name only". The married couple were often kept seperate until either the girl "came of age" (aka got her first period to produce children), or where just deemed old enough to start living together in the same castle, which wasn't until around 17-20 years old. The vast majority like the peasantry weren't married until their early 20s. Women in the peasantry often did have a choice on who they got to marry, unlike their noble components who were used as bargaining chips.

How true is this?