It's hard to say
MM isn't a mature title, and there are a number of reasons.
1. Themes are much more involved and intricate. Consider as just a quick example, the moon children. Their questions are quite deep, and don't suggest true answers so much as reflection over time spent in life. A prerequisite of that is having actually spent a good amount of time on Earth, so that these questions don't just glaze over the player.
2. NPC storylines are extremely complex. The entire couples mask arc adequately articulates the motivations, desires, fears, and love of just two characters. Add in the circus leader listening to Ballad of the Wind Fish, Igos du Ikana, and everyone else Link encounters, and it's apparent each one is more than just a shell. There is are complicated emotions behind every conversation, making the game a bit unreachable as a child.
3. The mood. The moon crashing, intense time pressures, general atmosphere of Clock Town and the surrounding burrows of Termina, even the name of the land itself imprints a solemn, quiet pressure to save... well, everything.
So yes, I see
MM as an extremely mature game, and I prefer it because of those themes. There is so much to parse out in each play through, I think anyone who played it when younger should try again to see how much more of the story manifests.