A man certainly could wear the 2017 Louisville Slugger XENO 13" Fastpitch Softball First Base Mitt: WTLFGXNRF17BM, however keep in mind that the glove is constructed with a female's hand in mind and the fit will be noticeably smaller than a glove created for a male.
The size of the glove depends on position moreso than age, with larger gloves generally used by outfielders than infielders. I would probably recommend a Youth model for a 9 year old, since that will be designed for a smaller hand size than an adult model, and have a smaller wrist opening and finger stalls.
The 13.00" length on this 2017 Louisville Slugger XENO 13" Fastpitch Softball First Base Mitt (WTLFGXNRF17BM) would function well for a high school aged fastpitch softball player. Generally speaking, I think that anywhere from 12.5" to 13.00" will work well for a high school player at first base.