The cruisers are a different animal than the sports bikes or even a standard. The engines and transmissions are set up for torque more than horsepower. My 800cc Suzuki Boulevard C50 has less HP than a 650cc Suzuki SV650 (I don't remember the numbers, but I do recall that it was by a pretty substantial amount).
Some people (on other forums, you don't really see it here) seem to think up to about 1100cc is OK on a cruiser. What you need to be careful with on a cruiser isn't so much engine size as weight. Too heavy and it can be awfully hard to control in slow speed maneuvers for a beginner. Mine is 611 LBS (before options, like my windshield) and my first couple weeks I definitely would have appreciated a lighter bike (and I most certainly wouldn't have wanted to go heavier). I think some of the 1100cc bikes weigh in at similar numbers, maybe even lower. Check the weight of the bikes you are considering and if it is under 600LBS, and you are very confident of your abilities after the training class, you may be OK. Regardless of the weight, there is no way I'd consider larger than an 1100, and I personally ruled out anything larger than the 900cc Kawasaki Vulcan (now I think I might have been OK to 1100cc, so long as the weight wasn't greater than my C50).
Now, that advice is partly because you are 40. Being a bit older, you are presumably more mature. You can still get in trouble on a cruiser engine, you don't need the HP of a sportsbike, it is just a bit more forgiving. Also, if you drop that 600LBS on your leg, you have a broken leg. I remember being a teenager and early 20-something, and I'm a high school teacher now, I would not suggest anything that big and powerful for a testosterone laden young man (I know, a double standard, but you young men out there, all that extra testosterone really can get you in trouble).
Anyway, back to specifics. The Honda Shadow 750 is a great starter bike. If you look at the reviews, while some may imply it is a little boring, they all seem to agree that it handles pretty predictably and is an easy bike to ride. They either imply or state outright that it is a great beginners bike. The Vulcan 750 is a slightly different style, more like an early 90s or late 80s Japanese cruiser, sit on one and make sure you like the fit, but if you do it should be a good bike to start on. The Vulcan 800 is a beautiful bike (I'm still a bit unhappy about 2 used Vulcan 800s that got away) and would be a terrific starter bike (I almost bought a new Vulcan 900 instead of my Suzuki). A Vulcan or Shadow 1100 might be OK (and used it seems the 1100s are a much better value than the 750s-900s, they seem to be about the same price and you get a bigger bike).
