First and last.
He may have done a trial cycle ride the night before. On some of his chosen route.
When a boy he may have gone cycling a lot. Boys have lots of energy.
If he went the sea wall especially at night he must have been familiar with the route.
Whether from childhood, walking Brambles, or a walk with Julie.
If for example he went to have a drink with nevill at WHF, he may have walked the route their in the summer and got a taxi back to bourtree for example