I'm a little confused, because I wasn't aware that there was career progression beyond Senior Developer. I mean, you can go and lead a team or something if you want I guess (in fact, I'm doing that at the moment), but most older developers I know have been and done that, and settled back in highly-paid, highly-respected, and much easier individual contributor / architectural roles. Looks like a good life to me!

The best developer I've ever had the pleasure to work with was a 50-year old senior developer. He cut his teeth doing a lot of C/C++ stuff back in the day, but was also (pretty successfully) leading the company's adoption of Angular. If you have a sharp mind, and you don't get stuck in your ways, then people will be begging for you to be their 50-year old senior developer.