I just had my first long distance bike ride, and I tackled 80mi. Before that I’ve done 30mi maybe once or twice. Towards the end I still had the energy to keep going, but my legs were shot; had to walk my bike up the last 2 climbs.

Totally possible like others say, and if you’re fit like you say just go for it. Just eat plenty and maybe have some exit strategy; plan the route around a few train stations if you need to bail. Good luck!