Just beware of the multitude of guys who I have heard will send agressively sexual messages. I don't think 21 is too young for internet dating.
That's when I started, and I met both my male BFF and my current SO through dating sites (and Ok C, respectively).
I think Po F attracted it originally since it first began with a set-up closer to Craigslist personals - everything was much more like open ads over profiles (which will also attract people who don't want to put effort into creating a profile).
It became known as a hook-up hub and that tends to attract certain audiences over others.
I really wish that I had saved the emails from them and some other sites before I chucked the email I used for casual stuff.
They really don't believe that you can be an actual, real woman looking for sex.
Customer service was out-right accusatory when I was asking about my issues.
Overall, it's pretty much a numbers game, it's all on who you can meet.
The biggest tips I can give you are to stay safe (trust your creep radar and red flags - stick to very public first/second dates) and to not take the creeps/idiots personally.
Most online dating sites just require you to be 18 . 23 now and I've been off and on over the past few years.
Paid sites like Match and e Harmony tend to be more for people who are looking for serious relationships with marriage as an end goal - the user base is also older (typically because you need the money to join at all).