Currently 26, started longer races at 23. bests of 4:19, 15:45, 54:35, 1:12:50, 2:37:30. I'm your average mediocre-post-collegiate runner with a demanding job and a social life that doesn't revolve around running. My experiences with high mileage training in the past have always resulted in stress fractures or conflicted with my susceptibility to genetically ingrained anemia, so I have sort of adapted accordingly.
Usually keep long runs at 30-35% of total weekly mileage but over a 16 week cycle (read: the 16 weeks before where I realize I paid for a marathon and begin to really increase my time spent running as to not totally embarrass myself) I like to have at least 4 runs above 20 miles with 2 of them over 22. Try to avoid taking gels -- or even stopping at all for that matter -- except for the really long runs. I am aware this philosophy directly conflicts with the advice of most experts that say long runs should only be 20-25% of weekly mileage max but I typically run only 6 days a week and don't double. Usually keep them around 6:45/mi pace, regardless of long run length, all the way through until last 3-5 miles where I generally like to pick it up closer to 6-6:10/mi to kill monotony.
I've never really hit "the wall" either. But I tend to run pretty evenly and don't think my last few miles have ever been more than 15 sec/mile off of my average pace either. I don't know if anything I have done in my training is helping with that, but that's my experience, for what it's worth.