[Disruptive_Dave]

SHIT NO!!! I'm 35, live in NYC, and one year into my first real startup that I co-founded. A few insights from my experience, as well as some challenges and advantages: 1) Everyone is younger than me and it's mostly humorous and enjoyable (I play much younger than typical 35yo's, tho). 2) I spent 10 years running a partnership marketing agency and I was lucky that I could easily translate my skills/experience/contacts to the startup world (mostly in biz dev). 3) There is a strong need for people with real-world business, people management, and corporate relations experience in startupland. You can probably run a conference call much better than these damn whippersnapper programmers. 4) The only real disadvantage associated with being 35yo in startups is risk mitigation. If you have kids and a mortgage, it's gonna be much harder to move fast and jump on opportunities. I am mostly unencumbered and that's crucial right now (actually moving for 3 months soon, as we got into an accelerator). 5) I'll never forget when a startup colleague (23yo developer) expressed bewilderment when I called him (on the telephone!) to talk about some business matter. He promptly explained that his generation usually does this stuff over gchat. I laughed. He laughed. 6) I've been thinking about this a lot lately; we only have one short life to live on this earth and it friggin flies by, so why not reinvent yourself a few times, professionally and personally? Assuming you're smart enough not to risk your/your family's future well being, go for it.

[Disruptive_Dave]

I should add: 7) Coming from the corporate/agency world, you'll be floored by the lack of basic business sense and planning found in the average early stage startup. Perhaps I was naive, but the severity of that mindset ("let's just make something flashy and get a ton of users and everything else will figure itself out!") surprised me at first.