A decision to specialize in mobile in 2009 would probably have even worked out for a 60+ engineer if they were good at it. The best way to combat ageism is to stay technically relevant. Good decision.
> The best way to combat ageism is to stay technically relevant.
As I get older, I find that is easier said than done. I still spend quite a lot of time learning new things, but I've become less interested in learning things that are immediately marketable. Learning yet another framework that is marginally different than the one I used on the last project is not the interesting pursuit it once was. At this point I would rather invest that time in something that might fundamentally change my outlook and understanding of the world, which is beneficial in a meta way, but isn't really something that you can specifically write down on a resume.
I think just showing that you are still learning makes you relevant. Displaying some level of intellectual curiosity will get attention, even if it isn't the exact framework or new shiny thing that is the latest flavor. Also shows that you can pick up new things.