Let me put it this way: I bought one in February of 2008. For the past sixish months, it's been really fat.
And now it just molted.
So, yeah, as much as a year and a half between molts, and it's still not as large as the only two females I've had give birth in my care.
Edit: thought I should clarify, it's V. spinigerus (or H. spinigerus, if you believe Soleglad and Fet).