How to estimate age of young snails

[latebloomer]

I was wondering if it was possible to judge the approximate age in months by the growth rings/whorls on the shell? I count five rings on my larger ones and three on the small ones. I notice new shell growth on the larger ones after ten days. What is the best size/age to go for when buying?

[Amy]

im glad youve posted this as ive been wanting to know the answer to this to :3 The only way i can think of is shell condition, but im probolably wrong.