There are many function in the congregations where age is not an essential asset. They have to give the capable youngsters a meaningful rule among the often boring old guard.
My advice to one of those 21 year olds: "Keep your Christian Innocence" . He is not a "newly converted man", but wt promotion could go to his head. who knows there might be good trojan horses among those not loaded down with wt doctrinal baggage.