Old enough to have been 19 many years ago. Its young on the timescale of the human lifespan, certainly, but by 19 one has the opportunity to be already fully established in society and industry. You expect people to be working on amazing things by that time. Any greatness that may come from that work does not seem particularly unusual to me.
I am actually quite surprised that there has been such negative reaction to my comment. When does one age beyond the "wonder years" if not by 19?