As you get older your immune system gets weaker and reacts to allergens less maybe that's why you feel better?
This is a pretty good article on asthma remission -
You can outgrow the symptoms, or triggers of it, but it seems they do question whether or not the changes in the lungs ever go away. The only way to know is to get a biopsy of the lungs, and that's not something done often.
I'm glad you're feeling better, though!