Define "young." Most Catholic parents bring their kids to Mass with them, even as teenagers.
I don't know of many parishes that rely on "young males" 18 and over to serve at Mass, so I'm not sure what your point is.
Even in the old days, when I was serving Mass, most Catholic boys were not altar servers, and only a handful ever darkened the door of a seminary, much less ever reached ordination.
This "well, we've got to restrict altar service to boys so we'll have future priests" is an old wives tale, in my experience.