Well, I am from the 'other side', that is distances. I was mediocre (which is generous) in high school and did not even think about competing in college. However, in grad school I started running again and found that I could ramp up rather fast (from nothing consistent at all for five+ years to 100 miles/week in 10 weeks and a sub-3 marathon in 17 weeks).
However, this does not address your issues because it is not the running that is a problem, it is running fast that is. Whenever I am coming back, what I find is that my legs 'remember' what is like to run at good speed but my body cannot do it, I cannot make the turnover and have the zip. It is frustrating until I ratchet back the expectations while I slowly ratchet up the capabilities.
Now consider this: At age 15-23 your worked hard and continually and got to a fairly high level. Now, after inactivity and a little age, you are sort of expecting that it will not take you years to build back up. Maybe it will not take you years to build back up but if you work at it at the same rate you did before after a year or so I suspect that you can be at a pretty high level, even if not like your college peak.