It's also completely incorrect. The average age of startup founders is 45, many of the best engineers in the market right now are older Millennials and GenX because they grew up in a time when you could still gain legible access to every aspect of computing in a home setting with PCs, which gave them an exceptional fundamentals basis which allows them to have a broader scope than specialists.

As someone who spent almost my entire career, until fairly recently, in startups, I would not consider age in any way a determining factor /especially/ for early hires. You need "adults in the room", because they will help to establish the bar for the remainder of the team as you grow, act as technical leads, and have a very broad scope of responsibility. The more experienced and capable they are, the better the quality of your future hires and the less technical debt you incur in the process of getting to product-market fit and growing to profitability/critical mass.

You should not (legally) have an age bias at all, but if you were going to apply one, the reverse bias is more rational.