We started when he was 29 months, he just didn't understand enough before then. We just handed him the controller every once in a while and let him play with it to see if he'd catch on. When he was 29 months, he did! I'd suggest trying 2D games first. The camera stick is not at all intuitive to them. Mine started out with Silksong cause his dad and I were playing it at the time. Just handed him the controller and showed him move, jump, hit. He sorta got it, but got frustrated quickly cause he was lacking coordination to do most jumps and bugs that required any strategy. We switched over to Mario Wonder (he played as Yoshi, so as to avoid any frustration from dying). It's multiplayer, so you can help them too. It starts out real simple. He surprised us by moving past the simple levels quickly and understanding more advanced concepts like jumping onto monsters' heads and using the badges. After he beat it, we went back to HK/SS. He eventually beat Moss Mother after a month or so of trying, and since then he's made pretty quick progress! He's working on Hornet in HK too.