No Boundaries, week 2

Ran last night on the treadmill to avoind the heat. When I looked at our upcoming Saturday group run, I saw that we will be running in 5-minute increments, walking in between. It must be my general state of exhaustion, but that seems like a long time. Keep in mind, I've run for 2-3 mile stretches at a time (not that long ago!), run 5 and 10K's, and recently completed a half-marathon without dying.

Why the bejayzus does 5 minutes of running seem like a struggle?

Am I really aging that quickly?