Good luck with Hammypie (such a sweet face!). Like you, my first hamster was a Syrian that I bought at Petco, and they also were unsure of her age, although they believed (or maybe guessed?) that it was six to eight weeks. If that were true, then Chiclet lived one year and 10 months. I think it's very possible she really was 6-8 weeks when I got her; she did seem quite young, small and active when I got her. (Within the first year she had more than doubled her weight!) But of course I'll never know for sure.
She started visibly slowly down about two months before she passed. I had taken her to the vet, but the vet couldn't find anything wrong. She never seemed to be in pain, and I hope that's the case. But she rarely ran in her wheel at that point, and her ears were always flattened down, as opposed to how perky they used to be. She also ate less and lost a little weight.
I do hope what you're seeing in Hammypie is a temporary situation. You're certainly getting good advice here from those much more expert than I am, and maybe those ideas will help. Best wishes on all this.
