My first bike was an 80s Xt250 and I had that bike for just about a year before I moved up. The bike was an amazing bike to learn on, and it had a low seat height of about 29 or so inches. The only thing that gave me a hard time when I got it was learning how to use a kick start. I'd say go for something small cheap and reliable. Something that you wouldn't mind if you accidentally drop, which you probably will,, it's just how it goes. As I general rule I have used, until you get used to riding, I wouldn't go over 500cc. You can if you want but that's just the way I've heard it.
Currently:1986 Honda Magna 700
Previously:2001 Honda VTX 1800 (Family bike),1980 XT250 (Modernized), 1985 Honda Magna 700
Dream: '96+ DR65, W650/800, Funduro