Your trainer is not gearing your program to gain muscle. He is doing the muscle building equivalent of taking your trt shot every two weeks .
There is science to maximize muscle gains for your specific genetic potential. You can continue to put on size and strength well into your 60's with the right program.
Train relatively intense stoping each set a rep or two before failure. Do 3-4 exercises per body part with 3 sets each exercise . (Higher end for big muscle groups like back and legs and lower for smaller muscle groups like arms).
Train 5 days a week. Sessions should always be less than one hour. Exercise selection and volume matter. The below works best for a healthy over 45 male. Your wife can follow the same program cutting a set off each exercise, boosting reps to about 12 and stoping about 2-3 reps short of failure each set.
Day 1 - chest
- Bench Press - 3 sets (post 1-2 light warm up sets)
- Incline Dumbbells - 3 sets
- Hammer machine type of press - 3 sets
Day 2 - back
- Pull downs to chest - 4 sets (post 1-2 light warm up sets)
- Seated long pulley rows - 3 sets
- hammer strength or like high rows - 3 sets
Day 3 - Rest
Day 4 - shoulders
- Dumbbell overhead press 4 sets(post 1-2 light warm up sets)
- Dumbbell side lateral raises - 3 sets
- Upright rows - 3 sets
Day 5 - Arms
- Straight bar curls -3 sets (post 1-2 light warm up sets)
- Alternate arm dumbbell curls - 3 sets
- preacher curls - 2-3 sets
- push downs 3 sets
- extensions -3 sets
- machine dips 3 sets
Day 6 - legs
- warm up with a few sets of light leg extensions and curls.
- Leg press 4 sets (post 1-2 light warm up sets)
- Hack squat - 3-4 sets
- Leg curls - 3 sets
Day 7 - Rest
You may notice that squats and deadlifts are missing -at over 60 I am not a big fan of squats and deadlifts for most people. The trade off for most is not worth it.
Do this for three months. You will make progress. Let me know if you need more help.