Posted: 08/02/2015 at 13:43
Hi John. I think doing a half-marathon would be very good, like a trial for the big day. Your times don't seem too slow, you might not even be the last runner to finish
If you choose a 'big' half, then there will be runners a wide range of abilities. Look on their websites and check the times out.
I think the general advice when training for a marathon is to concentrate on running. If you do need to rest up your knees, then you will have to do some cross-training which eases the stress on them.
I think you should follow a training plan for a marathon;most have a half-marathon race factored in. You may need to change the plan slightly to personalise it. But there should be a minimal of three runs a week, including a 'long slow run'. Listen to your body, and reduce training or stop if you have more than the aches that come with doing marathon training.