My daughter, is a "distance" walker/runner. Since she was a Toddler.
She could walk, with me, for BLOCKS on end.
My son, is a "sprinter." He could, since Toddlerhood, SPRINT like the wind. But he does not like, to do distances.
Both different styles... of "athleticism."
I know that, about them.
Your son is active. Typical boy.
I wouldn't worry about "endurance."
Activity types, are different.
Just like in adults.
As a kid, I was a track athlete.
I LOVED cross country and distance running. I was good at it.
I also could do sprinting real well. But that was not my favorite.
My son is 6, and loves tennis. It requires short BURSTS of energy. He is good at it. It is a good fit, for him. And he loves it. Versus, he does not like, soccer. Which requires running around forever all over the place. Constantly.
My daughter on the other hand... can go and loves, hiking. For LONG distances. My son does not.
They are both, different.
I know that about them and the type of their physicality.
I know... what "types" of activities, suit... them. Each.
And its fine.
I would not assume your son is "lazy."