It's really hard to find language partners in general (maybe 1 out of 10-20 people you message end up practicing languages with you).  Additionally, there probably aren't that many 18 year olds on this site to begin with, and normally people that age do not prioritize language learning as important.  With this requirement, you will probably find exactly zero language partners.

In my honest opinion, if you are worried about 50 year old guys asking you for pictures, just ask for female language exchange partners, and remove that age requirement.