Honestly it can't.  If you are in doubt I would stay away.

Nothing short of seeing her ID is proof positive, but if she has reviews you should be on reasonably safe ground.

Providers will not show ID my friend.  Fuck em & enjoy.  Well reviewed chicks on this site are ALL 18 or over.

1 - the agency will represent the age of the lady. This conveys a degree of protection to the "consumer" and places the onus on the employer.

2 - very young ladies *usally* lack the discipline needed to function satisfactorily in this sport. The agency provides the discipline and structure.

I've waited 10 minutes for an agency girl - but been NCNSd many times by young indies....

additionally "quality control" seems to be better -the variance observable in review scores is usually smaller with youngsters working for agencies vis indies

CMA: there are of course very professional and highly desirable young indies.

However, they are in my experience the exception and not the rule.....

I agree with the guy that mentioned an agency, just make sure its reputable. You can be sure they aren't going to risk the business for any underage girl.

Most of the ad sites, from what I gather, require a credit card to post an ad. I know that credit cards can fall into the hands of underage people but it would be doubtful.

If it really is bugging you I would simply inform her of your concerns by phone, then just go from there based on the vibe you get from her anwser.