My dad (in Italy) drinks his last espresso after dinner, at ~9pm, every night, and soundly falls asleep by 10:30am.

Perhaps he has a high level of CYP1A2? I am wondering if there's a cheap but effective method of measuring it.

I realise you said 'perhaps' but I have to comment on how much I dislike this kind of backwards reasoning. I used to compete in bodybuilding, and I heard arguments like this all the time. "I'm not making progress, I must have low testosterone", "I must not be metabolizing protein", etc. The number of possibilities is huge, you really can't say with any certainty what the cause is.

Most likely he just has a tolerance to caffeine from drinking it. It sounds like he drinks it all day.

May not qualify as cheap, but I believe 23andMe will tell you about the genes you've got which control your CYP1A2 levels, and predict your coffee intake accordingly.

That explains a lot. I really can't relate do other coffee drinkers describing their experience. I often drink 0.4 liter of black coffee to get rid of the late evening sleepyness when I want some hours of productive free time for gaming or programming before bed. When I try to sleep ~3h later the effects of the coffee are largely gone and I fall to sleep within 5 minutes. I guess I've got a lot of that enzyme. ;) (which is nice)

> I guess I've got a lot of that enzyme. ;) (which is nice)

You can't make an assumption like that, you have no evidence and there's many possibilities.