It really depends from person to person. You may or may not still grow after that age. I once gave a shirt I made to a guy who was around 19 or 20 at the time. The shirt was a bit loose and fitted perfectly. Now being 23, the shirt is too tight. And when I see him in real life, it turns out he had still grown.
I think a partial would be fine, though depending on how close you are to the age of around 18 a head, tail, feet, hands and surely a tail, would be no problem. Your hands and feet don't tend to change much in size or shape, whether you're 13 or 18, and a head... If you're worried your head might still grow (which I also doubt after a certain age xD) then estimate a slightly larger head, and fill the head in with foam or other forms of padding so it fits your current head.
However, a fullsuit not so much. It depends how old you are, though. You can always make minor adjustments to the body suit part, if anything. Usually it's the body part which still goes through some changes (not head or limbs, specifically the torso in this case).
Hope this helps