Hello and welcome!
Your pup is sure cute, if that's him in the picture!
I've had 4 labs (in addition to 5 other dogs in the past) and they've all been English style or show-bred labs. I guess I have a few questions and a few comments.
Always, if you're concerned about the health or activity level of your pup, I'd make sure he's been examined by a vet with whom you've discussed your concerns. Could he have achy joints or growing pains that make him less inclined to run around or jump up on furniture or into cars? Did you get him from a breeder who had done genetic and orthopedic testing on the parents to check their hips and elbows for soundness? Have you talked to the breeder about your concerns? Those are where I'd start to see what might be going on with your individual pup.
Judging from some of the other members on here over the years who have had labs who are more field-bred, rather than English style, they have always sounded wildly more energetic than any of mine. This is not to say mine aren't energetic, but they haven't had to play, play, play all day.
Not all labradors seem to understand that they are retrievers. Our first lab- nope. I'd throw a ball, he'd run over to it but never bring it back. Same if we threw it in water, he'd swim out, verify that's what we'd thrown, leave it behind when he swam back to shore. He did better with games of soccer where he'd be the goalie and stop the ball. Our 3rd lab is really the first one who would retrieve a ball and actually bring it back. The second one would only retrieve in water, not on land, but she'd bring it back to wherever she wanted, not to us.
Not all dogs want to go into the water initially. Are there any other dogs around who will go in the water or play along the shoreline with whom he might play or learn? Sometimes another dog is the best teacher. If you're hoping he'll jump off a dock or into a pool, that can be too scary at first. You might try playing along the shoreline where the entrance to the water is gradual. I wouldn't carry him out or pull him out into the water but let him learn to get into it. It can make a young pup more fearful to be forced into a situation like that.
Have you tried any obedience classes with him? It can be fun to do at least one round of obedience classes so you both learn how to communicate with each other and find some fun ways to interact. Even if you've had dogs before, this guy is his own self and may have a different way of interacting. And maybe you're just anticipating the more high level energy you were accustomed to with your previous labs.
Don't let your friends make you feel bad about your dog. There are a lot of people out there with opinions about dogs and how they should act or look or be that are off base. If you get him checked over by the vet and he's a healthy boy, then maybe you should feel lucky that you got a more chill pup on your hands.
I don't know what you're feeding him and how much you've fed him over the time you've had him. My 9 week old pup eats 3 cups a day of puppy food and my 4 year old eats 3- 4 1/2 cups of food depending upon which food I'm giving him. Neither are neutered, I know some dogs tend to need less food once they've been neutered to keep them from gaining weight. English style labs tend to be chunkier than field bred labs, so you don't want him to be too slender unless he needs to be for orthopedic reasons. Just an observation.
So, first I'd make sure the vet has checked him over, checked to make sure there's nothing of an orthopedic nature making him not run or jump or climb stairs as you'd expect. Check for worms, parasites, tick-borne illnesses. Discuss your concerns with your vet- they want to see happy, healthy dogs living their best lives, so I'd start there. If you're still in contact with his breeder, try to find out what his parents were like and see if they can offer any suggestions.
Those are the things that come to mind initially, not knowing anything else about your pup. So, let us know his name and let us know how things go. Hopefully he'll turn out to be just what you wanted all along, you just didn't know it!