If you already have your pro-rec, you should be fine, the only thing I've heard of that stops a pro-rec from becoming an FS is a medical DQ, or if the applicant does something stupid while waiting for the FS like get a DUI or something like that.
And yeah, I've heard of a few people that had to wait a ridiculously long time, but I'm pretty sure they were closer to the 20-24 age group, most of the time they'll speed it up when you're approaching max age. It's not in their best interest to make a qualified applicant wait to the point that they exceed the age limits, it would be their loss in that case too.