You are getting good advice here. I myself am an older player (80) but I haven't put the horn down for long periods of time. I would say the following: 1) your chops need to be in good shape to maintain a pitch properly. Getting back in shape takes time after such a long layoff 2) Use an electronic tuner (a phone app is good) and practice playing into it so you can hear when you're off. There are small devices that you attach to the bell of the horn to check on your intonation while you're playing with a group. Feedback helps.
M