Purity Rings? Should I get one?

Hi, I would like to get a purity ring for my 13th birthday (And a wetsuit). But My mom doesn't want me to marry young (Like in my late teens or early- Mid 20's). So I doubt I'll still be a virgin by the time I do get married. Are there any rings like Purity rings but mean you can't have sex until like 18 or 21. or should I get a promise ring. I took the pledge last year, meaning I'm never to take drugs, not to drink until 18 & Not to smoke until 18. I wear the badge a lot so i'lldefinitelyy wear the ring. Should I just get a purity and take it off if I do loose my virginity...But I wouldn't like others to know about my personal life............