You'll find two starter programs below. They are broken up by muscle group and are three days per week. You can experiment with splits, exercises, and the number of days per week. I suggest 12-15 repetitions and one to three sets per exercise for beginners (remember, you can gain significant strength with just one set). I've included more than one exercise for each muscle group. You can stick with one exercise if you like, or experiment with more than one. Use the principle of progressive overload and increase the weight when you can perform 15 reps easily. If you're using elastic tubing, start with the tube that you can lift 12-15 times to fatigue, and then increase when you get stronger.
Day 1: Chest (bench press with bar or dumbbell press, flies, pushups), triceps (bench dips, kickbacks)
Day 2: Back (bent-over rows), biceps (curls, standing or seated)
Day 3: Shoulders (lateral raises, front raises), legs (squats, lunges)
Here's a different split.
Day 1: Chest (bench press with bar or dumbbell press, flies, pushups), back (bent-over rows, pull-downs)
Day 2: Biceps (curls, standing or seated), triceps (bench dips, kickbacks)
Day 3: Shoulders (lateral raises, front raises), legs (squats, lunges)
It's worth it!
Resistance exercise is worth it. You'll gain strength, endurance, and confidence. It's feels great to feel strong, and I encourage you to give it a try! Remember, it's never too late to start!