My position is that if you ran a ton to get those times (100-120 mpw / at least 4 hours of time devoted to training related activity per day (roughly what I was trying to do in college)), the very nature of replicating a similar type of training to get back to where you were will be difficult since you probably have a full time job now and other, more pressing commitments. If you have the time to do it, then I don't think it is difficult. Now that I am in law school, I can't run as much, but still am able to win some slow road races by only running 20 minutes a day five days a week. I think will take you a while, but it is not impossible. A lot of people don't run their faster times for longer distances until they are older, so it stands to reason that you could touch the longer range times fairly reasonably if you have the time.