I turned 51 this Thursday. And I've gone from totally out of shape and 350 pounds to very fit (and 201 lbs., as of this morning). Working on building muscle now.
You are capable of doing more than you think.
I lift 6 days a week now- I used to do the typical 3X/week, but dropped the heavy intensity for more frequency and volume, but at a lower intensity.
I cycle 2 hours each day during the week (bicycle commuting to work; 15.7 miles each way, takes about an hour). Saturdays I either do intervals or an easy 2 hour or so ride, and Sunday I ride for 3 to 4 hours. Because I love it, that's all.
Recovery? No problem. Eat well, sleep well. My sleep quality has sucked for years, so I aim for 9 hours a night now.
I would suggest you drop the Running. Too much stress and injury potential for too little benefit. For cardio- walk, cycle, swim, something low intensity and low impact, with some interval work too (the 80%/20% rule). Cardio is over-rated though... At this point, your prime efforts should be centered on Strength Training. Your metabolism has not really decreased, rather your activity level and muscle mass has gone down. Check your Testosterone level and LIFT. Build muscle and watch your metabolism recover.
"The secret to happiness is freedom, and the secret to freedom is courage." - Thucydides, c. 410 BC
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