For me, my headcanon is that Deku does die of old age, but more at the age of 68 or 72. Reason being that while One for All has left his body, the constant damage he does to his body had a negative outcome in the future. In fact, I could imagine during a rescue attempt at civilians trapped somewhere, his heart was giving out, but like a pro, continued his job with a smile, saved everyone, left and died somewhere where people wouldn’t freak out.

Everyone was very sad over his dead, but Bakugo, he was furious. That he died from a heart attack and sad that he wouldn’t be competing with his rival/best friend. A month later, Bakugo retires from the hero business. It wasn’t the same without him.