Will concur w/previous posters (I'm 49 & saw this first-hand) and add an example. When I was considering my first marathon in '93, an older co-worker game me his training schedule, from Feb. 1981 Runner's World, Titled "How to Train for Your First Marathon"
Twelve weeks, 6 days a week, weekly mileage of 25/28/32/36/40/44/48/52/56/60/60/40. Longest long run of 18 mi (weeks 9 & 11), but 10+ miles twice or thrice per week in weeks 6 through 11. Races recommended in weeks 4 and 8. "Pickups" only speed workout recommended, sprinkled lightly in latter half of the schedule.
The assumption was you were in shape enough to handle this schedule-- and experienced enough in other races to ably move up to the marathon distance. Imagine a beginner's program like that today!
(For the record, I toned this one down. My co-worker, who ran the Twin Cities Marathon in 1982 using this schedule [without complaint], ran a 3:42 in his early 40s.)