Personally, I think who you do it with is more important than how often you do it.
I'm 16, I'm not a virgin. I lost my virginity at 14 to some one whom I loved more than anything. We did it once, occasionally twice, a week for about a year, so for the time our relationship lasted. Sadly, she cheated on me, ending it.
I have had relationships sinse then, including casual sex; however, it hasn't been as special when it wasn't with that one person.
Basically, I'm all for sex, whether it be casual or romantic, and it doesn't matter how often you do it with, only who. Say, if you had sex a lot within (For the sake f simplicity) a Month, but with only one or two (Or even three) people then that doesn't make you a "slut". If you have sex as regularly within the same month, but with five or six people, in my opinion, that doesn't make you a "slut" either, just simply seeking bodily pleasures.
To summarise, Casual Sex is pleasure for two people who aren't in a committed relationship, regardless of how many people you do it with.
[sub]Cheating, however, is another story...[/sub]