Before you buy something that large, maybe you could rent one for a weekend and just drive it locally to see how you feel with the handling and if you'll feel confident enough to take it out on the crowded highways.
You may need to take some lessons on how to drive a large vehicle like that if you've never driven anything that size. Older people tend to be a bit slower to react, and learn new skills, including driving ones. If your eyesight is good, your health is good I don't see why it can't be done.