Don't worry about the age thing, I'm going to be 59 in August and travel all over the Western US & Canada 90% on my own. Obviously we have bad areas in all major cities, but when you stop for lunch ask a local for the places to go or avoid. Talking of lunch, you can get a footlong sandwich for $5.00 at Subway, enough for two meals for many of us.
Motel & Camping is a great way to go, if its raining its great to dry your self and camping gear, get showered up. You can get motels from about $30.00 a night on up to $50-unless you are in a big city.
Stay flexible, its OK to set a goal of 300-400 a day, but don't book a motel you have to make it to and miss out on another day in Yellowstone. For your trip you might want to decide to go from New York to Vancouver BC, about 3000 miles on a direct route, divide the days you have, plus add a couple to get the bike etc, give you a good idea of how much a day. I use a sheep skin pad and carry 12volt pump along with a plug kit.
Make sure your UK medical coverage does cover you in the US. A simple visit to the ED here can set you back thousands.
Yes it an ambitious trip, but if its your dream do it-you don't want to be sitting in the pub when your 70 thinking if only......
Get a cell phone, if you have a UK GPS, get US & Canada maps. If you have name brand Garmin TomTom etc, maps are cheaper here, TT is selling US & Can for $60.00 at the moment. Get a Camelback water pack, you'll get temps well over 100 and you can dehydrate very quickly on hot windy days.
I always carry full good rain gear i.e. it is really waterproof and warm stuff. You'll be crossing some high mountain passes and it will be cold on some of them. Always check weather before you set of across anything above 3000' regardless of time of year.
Your common sense will be your guide on not offending anyone. There are a few, not so obvious words that could piss off certain races. Your normal polite Brit self will get you through any situations. As a fellow Cheshire Cat (Alderley Edge) I've never had any issues in the 20years or so of travelling around the Western US Canada etc.
Its your dream do it, you don't want to be sitting around in the pub when you are 70 saying if only................................
When you get to Seattle you'll be good for a beer & a bed.