In my family, it seemed to operate on a staggered scale -- presents up to 16/18ish, then small, more token gifts during university age. Presents stopped once you were out of school/gainfully employed, but at that point you could join the annual Christmas name exchange/begin giving gifts (no gifts were expected from the underage or students), and so receive presents in turn.

Thanks, however, were certainly expected at every stage, and omitting them would have likely resulted in my mother telling the unthanked relative not to bother next year.