My dad was like you. He bought an old 4 ft diameter sawmill. Used old case, with a flat belt to power it. It was more of a hobby/money pit for dad. He made a lot of sawdust. Used two 3 phase motors to replace case tractor. Tractor used too much gas. Then you need a skidder to move logs.
Go for it before you get before too old to have fun.
On the other hand, I know a man with a small sawmill. I take him wood, he gives me a small of the cut wood. That works for me. No investment. Besides I don't have that many logs and really don't need that much wood.