To be honest i think there is a sweet spot in development which is around 30's.
Before that you are usually too unexperienced :
After that , you usually starts to search for a comfort zone to stop learning all the time. Sure you have a lot of experience but you start to loose the passion.
Sure that's not always true , but sometime (most of the time ?) it is and that where the ageism problem in tech come from in my opinion.
I'm 50 and I've been learning a bunch of new stuff over the past couple of years and never shy from looking into something new (unless I'm really not interested in some (tech/language/whatever), which does happen). But yeah, I do know some people who don't seem to be willing to learn much more though many times they really shouldn't have pick this field to begin with.
Basically, if I'm in any "comfort zone" for too long, I get bored. :)
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