Swim laps daily in a Olympic size public swimming pool. Find one and pay. That's for cardio if you have bad knees.
Stretch first for a few minutes every morning also and do one set of push ups, one set of sit ups, one set of curls and one set military press and side shoulder lifts one after the other!!! You should be breathing hard and starting to sweat, rubber arms..
You can use the same 20 or 30 pound dumb bell weight for each exercise. Make it burn.. Makes it easier and you can do it at home.
I do that every morning but run and do stairs rather then swim, my knees are good.. That stretching, pushups and dumb bell work out lifting every morning takes me 10 minutes and keeps me toned.. I don't get sore either so I can do it every day.
I'm 51 years old.. Diet is everything though.. I should be a personal trainer for older men, I know my shiiit..
Make it a daily religion and never stop doing it!! Work up to it.. If you can only do a few reps start there, do pushups on your knees if you don't have the strength early on.. Do what you can to build up.. You will get strong and stacked in time..
THESE ARE THE EXERCISES BELOW, one set of each and one after the other with NO break in between every morning religiously will get it done!!!! Use some weight and strain, don't go easy!!
In one month your body will begin to transform I promise.. After one year you will be a stacked if your diet is solid..