I get why many people think Bonney is actually a kid, but personally I just don't buy it.

There's actually a pretty concrete way to determine Bonney's age and that's using Kuma's bear ears. Despite how he looks in the modern day, Kuma didn't have his bear ears as a child nor in the small glimpse we saw of Kuma holding up Bonney as a kid in Chapter 1063. Now, all we have to do find when was the earliest time Kuma was seen donning the bear ears to compare. This comes to us in Chapter 1066, when Shaka is explaining how Dragon, Kuma, and Iva were a part of a crew known as the Freedom Fighters that was the precursor to the Revolutionary Army. This image takes place at least 22 years ago since Dragon founded the Revolutionaries in the wake of the Ohara Incident. This proves that Bonney is at least 22 years old.

Also, on the topic of Vegapunk's clones. They likely can age since Stussy mentions when she sees the Seraphim alongside Lucci & Kaku that it's surprising to think that they're that strong while only being kids. That implies that they'll grow even stronger when they grow up. Stussy not aging could be explained by her Devil Fruit which is likely a Vampire or Succubus Mythical Zoan. Both creatures are known for maintaining their youth and prolonging their lifespans by sucking the blood/lifeforce out of people.