I've built a number of teams, and have repeatedly had the fortune of anchoring the back-end with a senior engineer over age 50. Experience matters, and it helps the entire team from a morale, design, and process perspective. You don't want to work for someone who doesn't recognize that anyway...

I wish I could be so lucky to attract senior candidates at my current gig; they're hard to come by at a trendy downtown-SF mobile commerce pre-series-A startup. Instead, I'm inundated with fresh code-bootcamp graduates. I'd be much more comfortable hiring those junior developers if I knew they would be able to sit next to a reliable senior teammate...

That said, if you're worried about being hired, start by building something on your own! You'll make yourself much more marketable if you show that you can pick up new technologies and actually release something.