I think over 40 is a bit low, they would have been in their late 20s when this started and probably would have exposed to it then.

I am 45 and joined here in 2013 and still follow Crypto even though I am old!

I think it depends on the person, I know people in their 20s now that still think the whole thing is a scam and also people in their 50s who are eager to learn about it. It takes a certain sort of openminded person to embrace Crypto who is able to see through all the noise.