Also no
In fact he may still have some growing to do. Our last two Syrians were both big and weighed 225g. It’s like people - the bigger you are the more you weigh. Large Syrians are great. Pet shop hamsters often tend to be smaller due to the breeding. You certainly don’t want to be worrying about him being overweight. Average weight is anything from about 160g to 225g or more depending on their adult size basically. It does sound like he is going to be a large Syrian if he’s 6.5 inches long. Sounds similar to our first hammy Charlie. He was a pet shop hamster but they bred their own which is maybe why he wasn’t small. We used to say his Dad must have been a guinea pig haha. I even went back to the pet shop and said are you sure this is a hamster - he’s huge! But he certainly was and a lovely big cuddly one with a lazy gentle nature - he would go to sleep on my knee.
Anyway - don’t start cutting back on food or anything - they really need a good diet to support growing especially in the first year and particularly protein for building blocks. They can actually get sick if they don’t get enough protein. Which hamster mix are you using?
It’s also why rat toys are better fir Syrians as large Syrians can get stuck in holes and tubes that aren’t big enough. You want to be looking at having at least 7cm
Diameter entrances/tunnels.