Ladycup

Ok, I really want to buy a ladycup and was just about to order it, when I realized something about sizing.

I turn 24 in a week, and it says to use the small size up until 25. Does anyone find this is really really true...? I don't want to buy this cup to only last me roughly a year. I am also very small/tight in my vagina (as my ob/gyn tells me every year). What would you recommend? Thanks!