I'm a 30 year old female who set out to break 3 hours in a marathon (CIM). I had never run a marathon but had run a 35:45 10k so knew it was feasible.
I ran 50-60 miles per week @ 6 days per week. One solid track workout per week and one solid long tempo or long run (alternating weeks). The other days were easy miles. I couldn't do more than that as I worked full time with two toddlers.
I think it's definitely feasible on low-ish mileage with some talent and a decent base build-up going into the sharpening stuff.'
I ran a near negative split 2:58.
Marathon training is actually much easier than 5k/10k training in my opinion. Good luck!