I got my turt as a hatchling from Petland, so I can guess her age to be about 1 1/2 yrs. I've recently given her a new home in a 55 gallon tank, but she's always been in an indoor habitat, with an occasional romp outside (with me supervising)for a few minutes in a garden.
Well mine are between 3.5-4" and they are a bit big for their age.. they should grow about an inch a year.. a bit more during the first year or at least that's what I've been told and read..