Okay it's online and it was written by a guy 15 years older than me but wow did that feel so good!

I'm not attracted to guys (although being held and feEling all safe in a guys arms...) it just feels so good!

Do girls get this all the time?

I don't know about online specifically but when a guy tells you you're beautiful they usually mean it. Unlike women, guys aren't big on false flattery. That's why so many of them end up with their foot in their mouth. Enjoy the compliment. ☺

Where online was it and did you talk to this person before or was it a random private message.

I mostly ask because yes, it can just be a nice compliment which is great....depending on where it comes from.
I know if your on like the Amino social media app for example and you get a PM from a lv 1 stranger saying that, you block them right away, it's EXTREMELY likely they are a ->-bleeped-<- (someone only after you for their own pleasure).

My point is, just be careful in that they aren't complimenting you for the wrong reasons.