I can think of two:
- Speaking multiple languages, and
- Perfect pitch
Both are more easily learned at a young age. Are there others?
Learning to drive. I’ve met a few people who didn’t learn to drive until their late 20’s or 30’s and there always seems to be some awkwardness to their driving. On the opposite side, learning to drive at 16 seems to encourage reckless habits to form, people I’ve known who waited until 18 have much better driving habits on average.