Well you really do have to look at who you are right now. Some younger folks know that they better get started on a 250 because they like to wring the throttle and go fast.
Some folks don't need the drama
and do just fine with bigger motorcycles right off the bat. I started riding in my late 20's on an 800cc machine and had no troubles. Successfully and safely moved up to bigger machines, but my favorite bike is my 750 commuter.
Don't limit yourself to cruisers. Sit on every bike the dealership and the local bike night locals will allow, even if you don't think you'll like it. The one that fits you will scream in your ear right away.
If you are a mature driver you will likely be a mature rider. Your driving record will tell the tale!
Let us know what you choose, we're glad to have you.....