I have been using a training plan for my last two marathons built for masters runners.
The common theme is more recovery is required. Both plans only had runs 4x a week with S/C 3x a week. That only gives me 60ish km a week.
On the other hand everyone acknowledges that mileage is king. The more miles you can log the better your time will be. Direct correlation between mileage and results.
I feel like my lack of mileage is a hard ceiling. Yet I want to make smart decisions to stay healthy and respect that I'm not 25