This is a very difficult topic. Since discriminating on age is illegal in most countries, there aren't (much) sites/platforms where age is an actual explicit factor. Generally speaking, startups/scaleups are more inclined to hire younger folks. Older companies are more open to hire older engineers.

The bypass might be, looking for companies that have a lot of engineers with 15+ years of experience. You can do so with paid LinkedIn accounts. I'm happy to help with some specific searches if you don't have a paid LinkedIn account yourself.