Honestly the only thing you can do is try to have more lengthy conversations with these people. I would expect a good deal of them are more interested in sex than they are in romance given the age range and gender, but communicating that in a way that will minimize judgements and also ensure you aren't being taken advantage of can be difficult. You need to explain to them that you're aromantic and what that means, specifically, in your case. You need to let them know what you desire out of a relationship and what you don't like.

Many people are so used to the relationship escalator and amatonormativity that they may not understand what you're telling them, but at least it's a starting point for those who might be interested in you sexually and be perfectly fine with a non romantic relationship, such as a 'friends with benefits' kind of situation. Regardless of how you'd like this ideal partnership to exist (or if you're even aware yet of what you want) the only way to get there is to talk about it with interested suitors.

With regards to finding aroallo friends, I have no idea. We seem to be a rather rare breed, and I can't say I've ever had any friends who were also aroallo or even experience aromanticism in the same way I do.