Drifting into a personal monologue, I know I am a lot better at learning now than I was 15 years ago. Learning advanced mathematics now is much easier than it was then (measured in the rather subjective unit of "amount learned / time taken"). Languages also are much easier. The only difference is the amount of time I put in now compared to the amount of time I put in then. If I was in full-time education now (instead of a half hour to an hour a few times a week) I would be yomping through textbooks and courses.
I think some of it is that I just know so much more now, and I've got so much more experience of joining knowledge up and making use of the combined result. I've also got so much more confidence in my ability to learn, and I know that if I'm struggling, grinding through does get results. I don't get demoralised, I don't wonder if I'm ever going to be able to understand it; I just do it.