I have anorexia & I have only had it since the begining of this year & im 29. It does not matter how old you are you can still get anorexia I have heard of people in there 60's & a small child of about 6yrs having anorexia. befor I became anorexic I was 9st 13lb & people would not think I was that heavy as I carried my weight well it sounds like you are the same I would tell them that you are greatfull that they care about you so much but You dont have a ED & that you would like them to stop going on at you about it.

Take Care