4 month old pitbull puppy too small...?

So I have an American Pit Bull Terrier puppy named Hercules. He's just the friendliest little guy and best puppy I've ever had 😇 he just turned 4 months old 4 days ago & he's the biggest in his litter.

A couple days ago a gentleman told me that Hercules looks to be too small for his age and told me that I should be very concerned. I love my pup no matter what size he is, but I want to double-check and make sure you guys don't think I should be worried...does he look too small for his age to you guys? Are there any issues I should be aware of if he is? He currently stands at 16.5" at the shoulder. I haven't weighed him in a while, but if I were to guess, I'd say between 28-30 lbs. I just don't know of any reason to be upset or worried if my pup happens to be too small and figured I'd ask....