I read a study that programming skill improves with age. And another that cognitive decline doesn't really happen until the late 60s if then. You might have so

I read a study that programming skill improves with age. And another that cognitive decline doesn't really happen until the late 60s if then. You might have some decline in motivation due to other reasons, not least anxiety about aging! If your colleagues who are enthusiastically porting that API were the same age as you, you would attribute your lack of focus to something else. There is no reason to latch onto age as the explanation.