I honestly think the job would kill Bernie. Just look at what it did to Obama.
But age in general is pretty irrelevant. My neighbor at 91 was climbing up on his roof to oil the rotary attic fans, and still crawling under his house to do some sort of maintenance job. He inspired me. My mom is 91 and can barely stand up with help. She broke both hips and never did the work to get moving again. She has a scooter and lives in an assisted living place that feeds them as much as they want three times a day. That and TV are her only activities.
The Social Security Life Table has useful data: I would say don't elect men over 80, because at that age their average life expectancy is 8.34 years. Likewise don't elect women after age 83, because their life expectancy is 8.04 years. I'm not sure what having a stent does to those numbers, but I'm pretty certain it's not good.