It is probably an impulse control thing.
Which many young kids, and even older kids, have a 'problem' with.
Even if they know what is right/wrong, they have impulses.
And this is a maturity thing.
I work at a school, and even see 5th graders with this problem.
I don't think it is "boredom."
It could be... just too much free... play and/or unstructured-ness.
Meaning, some kids, just don't ALWAYS do well, with a child-led atmosphere. Because, some kids, just do not... know what to do with themselves. They are young, and cannot or do not, lead themselves. MANY young kids, need, structure... to know what is coming next, to have a routine, and have things lead and instructed. And even a child-led atmosphere, can become "stale" or "boring" for a kid, because, they do not always know what to do... with themselves, and then hence, they start to bother other kids or do things they should not be doing.
Your son is also NOW, 5 years old. He is no longer 2. Even if he has been going to the same place for years. Developmentally, he is now, 5.
And maybe he simply has 'outgrown' the atmosphere and learning approach there. So, this is also a flip side, to "boredom." But is not boredom per say.
And at a certain age, some kids just need more structure... and more 'teaching' to... instead of the kid leading it. Some kids just do not do well in a child-led learning environment. There are pro's and con's to it... and per your child, and how he is, and his age.
Even in elementary and middle school and high school, there are some school programs... like the "I.B." school curriculum that emphasizes kid lead, learning. Not the Teacher "teaching." But some kids just don't do well in that... because, they need more structure and being taught, to. Just as an example.
My son went to a preschool with mixed ages. Some older and some younger than him. But he really loved it and was not "bored" or beside himself. It was not a problem. And it was a play-based preschool.
There are many preschools, at least here in my city, that accept children year round. So a kid can go to a different preschool at any time of the year. And per research that you do, you... can find a preschool that is more age, specific. Not mixed ages in a room.
Anyway just some thoughts.
Have you asked... your son, if he is, "bored?"
See what he says.