It has nothing to do with age. 39 is the new 29 nowadays. If you’re not sporting fake teeth, a cane or a prescription for Viagra, your age doesn’t matter much when it comes to buying a simple round of drinks for strangers. People will take anything for free!
What’s creepy is the way you handle it. If you buy a round of drinks for some chicks, converse with them for a bit and then go back to minding your own business, you’re golden. The ladies will appreciate that not only did you buy them drinks, but that you were a gentleman while doing so. You shouldn’t intrude on their night out – unless they make it clear they want you to.
Truth be told, if one of the girls are interested in you, they’ll break away from the pack to talk to you on the side.
Now, if you buy a round of drinks for a group of girls and then proceed to hang all over them and act as if you’re entitled to something simply because you paid for drinks, then yes, it’s creepy. If the girls are making faces sideways, rolling their eyes at your sweaty face, and don’t say another word to you other than “Thanks for the drink”, you’re dangling on creep territory.
Don’t be that guy. Buy ONE round – and hope that there’s a girl sweet enough to buy you one back.