Besides medicine, probably the hardest grad major is physics. Pure math may come close, but physics actually takes the most difficult math (Calc 3, differential equations, abstract algebra etc.) and then applies it to the physical world.Think Einstein, Musk, while setting aside his politics.So imagine my surprise when I stumbled across a story about a former physician who went back to college after he retired, Brown University no less, and got his PhD in physics; and he’s only 89, set to turn 90 next month.Rock on, older dude. I don’t know what it is, but this age deal is playing ...