Hi Probably Jonathan:

I have no expertise in terms of strength training, but I can tell you something about cardio that is UNIVERSALLY agreed upon. This is VERY rare in exercise studies, so it's important to seep in mind.

Lowering blood pressure: If you don't have problems with hypertension you may not think this applies. But the odds are very high as you go into your 60s and 70s you'll want to do this rather than take pills.

Mild to moderate cardio is BETTER than weight training for lowering hypertension (and weight training "can" be helpful for some in this regard, though not all)

So for example, Jan (my wife) and I go for a 30 minute walk every day. We do have some fairly steep hills in our neighborhood but you can still benefit from walking on a flat surface.

I find if I miss just 2 or 3 days my BP starts going up. That's anecdotal but the research bears this out. If you can't do 30 do 20. Can't do 20? do 10. Rowing is good, but there's something special about being outside and moving (yes, the research bears this out, especially if you have any attention problems).