If he really wants this then take him on. But charge him accordingly. Free is not a good price. You are already a professional. Plus payment will make him value the time you spend training.
#1. Tell him in order to reach his goal he needs to train with you for a certain period of time. You evaluate him and decide this.
Lets say its 3 months. Decide how often he needs to meet with you. Lets say 3 times per week. That would be 12 weeks(3 months)x3(sessions per week)=36 session.
Minimum would be 70 per hour. You seem to have experiance so I would say your price should be at least $100.
So 100 x 36=$3600. If he needs to pay monthly thats fine. As long as he's getting results he'll keep coming back.
For $3600 you are going to be:
1. Adding years to his life.
2. Making him feel better about himself
3. Getting him stronger.
4. Making him look better.
The benefits are too many to name. But thats how i'd price it.
I'd also tell him that if he brings a friend, then you'll only charge each of them $75/hour.
-So he'll save money,
-he'll have a friend to compete against during the workout,
-you'll have an extra guy to help you spot if you do heavy squats or board presses,
-and you'll make more money! Which will make you really motivated to bust ass!
