beso is right. It gets harder to keep the weight off as you get older. Look at most older people. They are not lithe and trim. If you are a man, I would say that personally, 9 stone is very small and at 10.5 stone you are probably a bit more meaty and masculine. I have a friend my age (39) who is worried cos he used to be 9.5 stone and is now 11- but he is SO much more attractive now, a bit heavier. Similarly I have another friend who is in his 50s and now has Parkinsons. The drugs have increased his appetite and now he is 11 stone, but before he was a tiny little bird-like man, not attractive at all, in my view!!
My Grandma was a tiny lady all her life and then suddenly put weight on around her middle in her 60s. She hated it and said it was impossible to shift. Middle aged- spread I'm afraid. Grannies with washboard stomachs don't exist, to my knowledge.