In my experience and the research I've read, you've almost mentioned all the top relevant reasons: alcohol use, stress, and reduction in sleep (kid being born). It's unlikely to be age.

I'd highly recommend last year's "Why We Sleep" [1] for more info on memory performance and how it's impacted far more that you'd suspect by full (and quality) sleep, which is in turn impacted far more than you'd suspect by alcohol and stress (not to mention kids).

[1] https://www.amazon.com/Why-We-Sleep-Unlocking-Dreams/dp/1501...