Get a pair
Like the odd other I reckon you could be better going for a couple of bikes. Let the old Shelia, and the kid (once licenced, but she's not to young to start learning. I started riding when I was eleven) ride their own. The two up malarky is ok for a bit, but I prefer riding solo. Go on your own when you want. Ride in pairs when you want company.
Why not go for something like a Honda CBR250R and a CRF250L. OK only a quarter litre, but they would cover your bases (on and off road) on relatively lightweights that are fun to ride. They are highway capable, and byway in their element.
The pair could be had not much more than a just one bigger machine; less than something exotic. At 70 mpg, and generally cheap to run, they would cost not much more to own than than a single big bike.
there are old motorcyclists and bold motorcyclists
but you seldom meet an old, bold motorcyclist