Worried about my rats health

[Capistrono]

I have 3 rats, Gabe, Watson and T.K. I got Gabe from a pet store so I'm not sure how old he is, but I've had him for about 8 months. He isn't very active and mostly hides in his favorite nest box all day long.
Now, whenever I let my rats out, I just open the cage door and if they want they can come out, and they free range in my room. Watson and T.K. almost always are very excited to come out and enjoy the time. Gabe, however, never seems interested. Sometimes I pick him up and take him out but he always seems unhappy when I move him from his favorite hiding spot.

I'm worried about Gabe's health, both mentally and physically as he isn't very active. I'm also wondering if it's better to let him stay in the cage or if I should be forcing him to get out of it occasionally.

[Ratties rock the world]

If I were you, I'd make him get out of the cage occasionally because rats need exercise.
But other than that, one of my rats just loves hiding in his cage and is very lazy. A lot of male rats are like that.

[ema-leigh]

Have you ever spied on him to see his energy levels at night? I know lots of male ratties are lazy, especially throughout the day.

If you are going to force him out, do it during the evening or as late as possible, so you know you are not distributing him too much. You could also make coming out appeal more to him by letting him have yummy treats + veggies only outside the cage.

[Capistrono]

My other two rats are very young and active so maybe I'm just comparing him to them too much.

I'll try giving him treats only when he's out and see if he doesn't mind it too much. Thanks guys!