I'm gonna guess you aren't Catholic. :^P
He isn't actually saying childlessness is a sin; he's saying that breaking the natural connection between marriage, sex and childbirth is a sin. There's nothing in what he says that would say that chastity or impotence are sinful.
“We grow up by having children. Without that responsibility, we have a generation of perpetual adolescents just growing old."
Put more precisely, it is the experience of participating in the act of creation through which we are drawn closer to Godliness, for if we participate in that act with our hearts open to understanding God through it, we can experience a reflection of the sacrifice, joy, love, and compassion that the Father has for his children. Thus, we "grow up" spiritually.
Ah! So, for example, the apostle Paul was an immature adolescent, spiritually speaking.