I would personally argue the CMC are closer to 10-12 in human years, so I'd think the latest a pony would get their cutie mark is around 16. One or two late bloomers at maybe 17.
Oh no, if you have work tomorrow go to bed man! Don't stay up for me, I don't want you to be absolutely miserable when you have to go to work. Trust me, I've been there before. Ever pulled an all nighter before the second day of a new job? It sucks. X_X