S.H.
Teach him how to problem-solve.
He whines? Grumbles? Complains? Is bored?
Tell him "problem-solve that...." and have him come up with things to alleviate.. his said complaints or whining. And discuss it with him. Praise him for coming up with good ideas.
My son's teacher, teaches her kids that and that is what I do with my kids.
Hence, kids "learn" how to become proactive.... and self-reliant. And self-aware. And become, able... to problem-solve, many things or situations.
Because, learning how to come up with "solutions" is a skill. Then an aptitude. Then, more of an instinctual reflex.
Teach him that... now. He is old enough.
Then maybe he won't whine and complain so much. Because he will feel more self-reliant.
And maybe, he just wants to do Legos. Not the gad-about type. Either.
But still, teach him how to problem-solve... there are so many ways, not only one way, to do something or solve something.