It’s not clear how much time has passed since season 1, but we know that Grogu was about 50 then. Considering how long Yoda lived, Grogu is still a wee pumpkin. He can’t speak and acts like a kid, stealing candy and using his Force powers to spin in an office chair. However, we don’t know exactly what his maturity level is compared to a human child. He seems like a baby, but he’s clearly smart enough to understand Din’s lesson. He’s scared of space whales (they’re called purrgil) like a tiny kid would be, but perceptive enough for Luke Skywalker to grant him the adult choice of continuing his Jedi training or returning to Papa Mando. He’s emotionally mature, even though he’s a tiny snuggle bug.
How long did Grogu study the Force to have the kind of mental control he demonstrated on Mandalore? It’s not entirely clear. He trained in the Jedi Temple on Coruscant for an unspecified amount of time, and we don’t know how much he learned before Order 66 was enacted or if he was practicing after being rescued.
Though it isn’t exactly crystal clear how long Grogu studied with Luke Skywalker either, it’s been a bit of time, according to Jon Favreau. He said something in a recent quote about it being two years, but he might also have been speaking about the amount of time since the end of season 2 actually aired. Still, when we visited Greef Karga (Carl Weathers) on Nevarro, the town was built up in a way that would likely take years, and the Armorer (Emily Swallow) has clearly recruited a large number of followers. Some time has definitely passed, and he could have done a lot of training.