One valuable asset for a startup is domain expertise. There are two kinds of domain expertise: academic knowledge, and experience in the field. You can get academic knowledge when you are young, but experience takes time.

I've only been to one tech conference, but it made me feel better about just getting into the startup world in my late 30's. One demographic I saw at the conference was a whole bunch of young, really smart developers who had no idea what to focus their skills on.

People with strong experience in a particular field can have a valuable perspective on what kinds of problems are worth solving in their field. They also know what solutions have been attempted in the past, and why those solutions were not ideal. This kind of knowledge can help a startup avoid the mistakes people have made in the past, and create a more effective product or service.