1. Exercise is important for all of us. I am the same age and spend 90 minutes at the gym 5 to 6 days a week. I do 30 minutes of cardio and then a bunch of different exercises, about half related to my legs. I do a lot of core work and rotational stretching. When I hear people talk about the limits due to age, it gives me more inspiration to prove them wrong.
2. I have several old leg injuries but try to walk at least 9 holes every week. In the winter it is a great way to stay warm and keep the blood flowing. In the summer the arthritis subsides a bit and I mostly use a cart because I am riding with somebody, but I still walk most of the fairways. I think there is an advantage to walking as long as you body is in shape to support it.
3. Not much on speed drills, but a lot of rotation work and swing mechanics.
4. I am a firm believer in outdoor golf, so don't do much indoor training. Besides, my ceiling isn't conducive to indoor golf. Tried it once and had to replace the ceiling fan.

I'm trying to find programs as we speak. I'm 51 and want to improve my fitness level.

TPI has great workouts and drills.

1. I use TPi programs for golf specific exercises amd stretching. Pumping iron alone doesn’t increase rotation. I’ve been evaluated locally and updated my routine with an online coach (COR Golf Fitness) as I am self motivated to work out at home. Titleist, with Dr. Greg Rose developed routines for professional golfers - hence Titleist Performance Institute. The evaluation determines your weaknesses and you get an individualized routine. TPI certifies local instructors - likely there are instructors near you - MyTPI.com.
2. Only if 18 holes tires you out. At 75, the majority of my rounds are walking. Walking up to a green can help you with reading the green.
3. See #1. I don’t, besides TPI routines to encourage fast twitch muscles. Maximizing rotation and strengthening core and buttocks are as important to increase swing speed.
4. Late October to mid-April is a long time. I use simulators both for working on swing adjustments and just for fun. I don’t take the results very seriously as mats eliminate the worst fat shots. Putting is just not real, although I do practice technique on a 10 foot mat in my house.
All in all, my golf fitness carries over to my day to day life. I walk 2.7 miles daily (weather over 25 degrees…) with the dog and with arch supports and the exercising, my knees are no longer an issue.