Prove it with some research. The current research shows that people really don't make their best contributions to their field before 35-45.
And, to be fair, I see more young people who attempt to hit the screw with a hammer because a hammer is the only tool they have.
Look at someone like John Carmack - before he was 35 he had done Command Keen, Wolfenstein 3D, Doom, Quake 1-3. Guys like Steve Wozniak were basically out of the business by the time they hit 35. Linus released Linux when he was 22, and started git when he was 35. I doubt guys like Marc Andreesen have written much code since they hit 35 as well.
So, basically what you're saying is that young people can churn out software where you can undo your huge screwup, but if you have to get it right the first time like hardware, then you need some experience.