Hi,

You can always train hard or you can take it easier and
put the miles in, the latter will take longer in the saddle,
and more hours per week, but either way you will get
there eventually if the speed you want to go at is
reasonably within your compass.

Personally I go for the mileage option and never try
very hard, I learned that from my running, just rack
up the weekly mileage to be overall fitter / faster.

The take it easy relatively high mileage option also
means you will end up burning more calories then
shorter, high intensity, bursty interval type training.

I personally think the latter style of training is OK for
running for short sessions for older duffers, but the
magic of a bike for the older is you can do it for
hours each day, you can't running or swimming.

rgds, sreten.