Is it bad for a 21 year old and 16 or 17 year old to date?

I am a 21 year old lesbian( a tough girl but attractive ;), anyway I recently joined a dating service website where you can IM, flirt, chat, etc. I've talked to many hot women on there and most of them really like me. You have to be at least 18 to register on this particular site,by the way. The problem is I've chatted and flirted with a couple of girls who had age 18 on their profile but they are actually 16 and 17! I wont date any younger than 18, and I really don't want this on my conscience. Sadly, I really like them too. I am so confused, help please!