4 of 5 of the biggest tech company founders were in their early 20s. So the biggest ideas clearly slanted towards young visionary founders, but the statistics do skew back towards older founders for all but the largest companies.
Microsoft, Google, and Facebook indeed were started by young founders. Twenty years later Google might be the only meaningful one standing. Time will tell.
It's been more than 20 years and Microsoft is still right there.
EDIT: Page was 25 and Brin was 24: https://en.wikipedia.org/wiki/Larry_Page