Dry kitten food

[cats4ever]

Iams kitten food is not a bad choice, but Iams has been linked to obesity problems in pets. Maybe your vet was referring to that.
I have always raised my kittens on Purina, and they did great, and, like you, I have never had an overweight cat.
Now they're are all seniors, and they're eating Purina One dry and canned Fancy Feast, except my 18 yr old who's on a kidney diet.
It's hard to overfeed a kitten since they are so active.
I guess your kitten is neutered. This slows down their metabolism, and overfeeding can make them overweight.
Do you free-feed, or have set meal times?

[Doug_FL]

I free feed my kitty cat.

[cats4ever]

Once you transition him to adult food, you might want to change to set meal times.
Other than the possible inconvenience factor, it has only advantages.

[phesina]

Yes, giving him set amounts of food at set times of the day is the best way to keep him from getting overweight!