Biologically, maybe, but only a little and it won't explain the feeling that it's a lot. I don't think it has much to do with any age related cognitive decline

Biologically, maybe, but only a little and it won't explain the feeling that it's a lot. I don't think it has much to do with any age related cognitive decline and mostly to do with more responsibilities, more things competing for your time and an objectivity that causes you to have different priorities. As I've gotten older I've only had more and more things competing for my time. I have a family, a home, hobbies, etc. I just can't devote hours and hours of uninterrupted time. With experience there's a lot of "ain't gunna need it" and if I do I'll learn it then. I've got plenty of stuff that I sank tons of time into in my younger years that only faded into memories and didn't turn out to be very useful. As far as tech goes you'll see enough stuff come and go that sinking that much time into it will feel like a waste. Remember SOAP, SOA, XML, XSLT, EJB, CORBA, MapReduce, Mesos, Java Applets, etc? A lot of what you're doing now is going on that list.