This was very much my experience with computer science. When I first studied computer science in middle school at age 13, I could only understand simpler algorithms like quicksort. I simply couldn't grasp dynamic programming. When I studied it again at age 19 (after having learned a couple of more programming languages like C++ and Python and Haskell, as well as taken some classes in mathematical proofs), it became much easier to understand. And then it was around age 22 when I could solve competition-style dynamic programming problems with ease.