I Am A 6'1" 340 Pound Man. I Am Struggling

I am a 6'1" 340 pound man. I am struggling with my weight. My knee and ankle are in bad shape and I am wearing a knee brace and an Arizona brace on my ankle when I am on my feet for prolonged times at a part time job. I am 66. I was on metformin and have been off it for a number of years now. It has occurred to me that I don't remember or know of many 80+ year old men over 300 pounds. The question I have been pondering is mortality. Is there a average life expectancy for a man of my description?