I met a lady who is 72 in Calgary HI hostel.
Besides, from what I see on the brochure, family is welcomed in this hostel. You better call for reservation and probably you can get a whole room.
Note: when using this website to search for Quebec city B&Bs, choose Quebec province first, then search using key word "quebec" instead of "quebec city".
I think to find a good B&B near Old Quebec is good, it is worth the additional 20$, probably you can find one with 70$ if book in advance. Enjoying the lower town's evening and save the time to travel to your lodging place is worth it.
Along highway 138, you will find some motels called, there are also some B&Bs along the long "Avenue Royal", but there was some construction work when I travelled last time, have to switch to 138 to go back to old quebec.
Another item worth mentioning is that, you have got to see the "Caynon Ste Anne", it is much better then the great fall.