I'm 46 & just started playing tenor sax. I try to practice for a hour a day but after 45 min.s the middle G gets pitchy & can not hit that note. Tried other sax same thing happens. Is it my embouchure or am I practicing to much for a beginner or is it something else?

The octave G is on the edge between the two octave vents & is always a bit sensitive to breath support & embouchure changes. (Even as an experienced player this sometimes happens to me - especially if the reed is a bit soft) The most likely thing is your muscles getting tired. For a beginner an hour at a stretch is a lot of playing - maybe practice for 2 or 3 shorter periods in a day if you can. Good luck.