Well, it usually takes about 6 months for the bristles to start coming in (or is that "coming out?"). I've had my two for nearly a year and I think they've stopped growing. Or if they are still growing, it's deadly slow now and there's no way for me to see it. I do think my female grew larger than the male in what seemed like overnight. They were the same size for forever, and now you can tell which is the female just from the shadows, 'cause she's so much, well, thicker and wider.
I have a 6-month baby who's just over half the size of his parents, if that helps, lol. I guess the parents are about a couple inches, maybe more, but I'm terrible with judging size with just my eyes, and I have no clue where a ruler is, lol