There is very little in common between software development and company development.
Yup, and "age" has nothing to do with either, experience does. If you work as a programmer, then as you age you should get better. But not because you are older, but because you are more experienced. I am an old guy (mid-fifties) and on my fifth startup. One was a clear success, the current one has been partially successful, and the other three were complete failures. I learned much more from the failures. The first was when I was when I was thirty, and I have worked at startups ever since. My situation is different in a number of ways: I was on the founding team every time, and my wife is more of a workaholic than me, so I am under no pressure on that. The biggest risk with a startup is usually financial, but if this company already has 300 employees, they either have plenty of funding or solid revenues. Your gray hair can be a significant asset to a startup. Investors like to see some adult supervision, so you should try to take on the role of the wise old veteran when you meet with them. Don't worry about the "social activities". If you pull your weight at work, the twenty-somethings aren't going to care if you go snowboarding with them.