Interesting, do you have any good links for this?

I can have a coffee a bit before bed if I really want. I also used to think I had a "high metabolism", but don't say that anymore since it comes off as kind of bogus.

Unfortunately no. It's my inference, given that 23andme didn't find any genetic indicator (CYP1A2) for slow metabolism, which is in line with my experience I got more sensitive over time.

So it must be some other mechanism that diminished enzyme production. Some of my liver (were those enzymes are produced) values were elevated over the last few years for no good reason, and I suspect the two could be related.

It's a bit annoying, as I'm reacting to trace amounts of caffeine in coffee, tea or chocolate, but I'm more worried about all the other, possibly carcinogenic, environmental toxins my liver won't be able to filter out.