Hi and Happy Christmas
It can be ridden in a day staying on the roads though I rode the C2C solo on my Mountain Bike in 2005, I was 59 then.
I caught the train from Derby to Whitehaven on the Monday, rode via Whinlatter Forest route to Keswick that afternoon and stopped the night in Keswick. Tuesday I rode the Old Coach road route and over Hartside to stay in a B&B at Garrowgill. Wednesday I completed the ride to Tynemouth and stayed overnight in the Grand Hotel. Thursday I caught the train to Newcastle and from there back to Derby.
Do your homework, prepare well, both stamina and equipment and arrange to let someone know where your route is taking you for the day. The route is very well signposted with plenty of places to stop for breaks. I quite fancy another crack at it!
Ps: I bought the official C2C route map.