In the series Caffrey is a technical expert in just about a million things.
Paper and ink documents? Painting, in any medium? Miniature painting? Sculpture of multiple types? Glassware forgery? Alcohol forgery? Art restoration? Non destructive encasement and removal of smuggled items? Safe cracking? Gem forgery? Multiple langues? Etc. etc. etc
The point is, while there is some crossover between his areas of expertise, many of them are fully independent areas of study in their own right.
So, to become expert in so many things, Neal would have had to spend a lot of time dedicated to learning them.
My headcanon is that when he was younger, he spend a good 4-6 years just working on stuff for 16+ hours a day. And then after that learnt some stuff a bit slower.
They say you need to spent 10,000 hours doing something to become an expert, that's just under 2 years of 16 hours a day. So a few years intensive study to become expert in a few things, and then a few more years more slowly becoming an expert in others, while also keeping up with his homework.
Bet he has friends in all different countries he regularly calls to keep up to speed with the languages he speaks. Bet he learned a new skill while in prison too.
The show just never mentions how much work actually goes into becoming the font of theoretical and practical knowledge that Neal is. And honestly, Neal is the type to have been a recluse for a few years and never bring it up again.















