I studied piano playing from age 11-19, then I had to quit municipal music school and went to the university. Engineering studies. I later bought a digital piano but I practiced most occasionally and during the last two decades I'm afraid I played very little altogether. When I decided to make a "comeback" near the end of 2011 I found out I was in a DREADFUL shape. I couldn't play anything. I was 45 years old.
Today I have regained my old "skills" and surpassed them big time. I play pieces I could not even dream of learning, ever. I have a much better practicing technique today than before and most of all - I think I understand the music so much better now, because I have matured.
I used to focus a lot on technical exercises back in my teens and I found it was very boring. Today I integrate my exercises in my learning process with new pieces. If I work with a piece in, let's say, c flat minor, I might do some scales in that key, or some other simple finger exercises. But I think the funniest way to exercise is to pick parts of the piece itself and make little variations of them, create my exercises from there if you like. I have noticed that I play with better confidence if I have allowed myself to "trash" the piece a few times.
You learn a bit differently when you are an adult compared to when you are a child, but that doesn't say it is a worse way. It is just different. I would say that I plan more, evaluate more and play less today.