Although there will be anomalies, age grading was designed to allow runners to compare their performances across different age groups. Presumably if you just want to compare your performance against your age group peers, you'll look at the times
Have done this 4 times and used road shoes, even the one year when it was very wet and muddy. Obviously it's fairly flat except for the bridges (quite a lot of them!) and they tend to be concrete/tarmac so on the whole grip isn't a problem.