2009-06-27 Sat - The Maths Geek ride √-4 - London to Oxford

At your age and level of fitness - hardly.

I did the 260k aged 50 and weighing 15 or so stone only 12 months after taking up cycling. I think that you could easily double the distance particularly if there are no cobbbles.

I would, however, recommend some very long training rides and great care over nutrition and hydration.
Sounds all good then, I'll be doing at least a couple of 200k rides before hand and not drinking has improved my bodies condition already. By July it'll be even better.