Sensible or not? here are the facts...?

Boyfriend wants to ride to Sturgis, SD, wants me on the back. From Amarillo TX to Sturgis, in two days, about 400 miles a day. Yamaha V Star 650, LowRider. We are not bikers, bike is trustworthy... Then, tour around on the bike for three days and head home again. Will our s make it? We are 50ish...never did this kind of thing. Back seat feels pretty hard to me and he is just crazy to go...Any suggestions??? Thanks!!