When my son, 6'3", was in college he had a buddy give him a non- running '78 Honda CB750. Over the previous few years he had hinted he should be able to ride one of my bikes. Remembering how I used to ride when I was that age I was not too keen on allowing that to happen. I must have been more forthcoming with expressing my desires about he not riding than I could remember because sought out his mother's advise on how to tell me he had a bike.
Anyway, I trailered the bike to my shop and it turned into a fantastic father/son project. We approached it from a restoration point of view. We tore it down to the frame and rebuilt, sandblasted, painted, and polished every component. While I funded the project, the time together and the education he received was priceless. He has since restored three more bikes of similar vintage and is now building a custom turbo charged 900+ cc engine out of 750 cc engine.
I share this story because it ties into some of the comments posted already: an older bike teaches the maintenance need, is typically lower cost, the 750 is a decent starter bike in terms of size and availability of parts, and isn't obnoxiously powerful when compared to the crotch rockets. Plus the investment in the time and effort in taking a junker and making it look and run like it did when it was new might lead to more careful riding to avoid damaging it.