Minimum wage is a federal statute. Certain tipped employees are exempt from the law. The hourly wage that servers make is usually entirely consumed in income taxes before the check is even issued. The only money they "take home" is garnered through
Tips. Even some of that is usually due back in April (if not withheld by their employer) as the $2.13 hourly wage is not enough to cover anywhere near their entire tax obligation for a year.
I would be shocked if your friends are actually making $7.25 an hour working at the type of restaurants you described. $2.13 an hour is an industry standard as far as I know.