Sometimes I come across people that say 'I've been playing guitar for 20 years', and it turns out, the best thing they have to boast about from that 20 years playing guitar, is that they've been playing guitar for 20 years.
They aren't looking down on you because you are 19, they are looking down on you because you dress stupid, and can't grow a beard, and are probably on their lawn, like all the other young people.