All of the 10-mile distances are milestones for me. 20, 30, 40, etc. I remember how excited I was back in my 20s the first time I did a solo ride in excess of 50 miles. Now, at 56 years old, that's still a major one for me. The other one I recall from way back in my more energetic youth was the time I broke 30 minutes in a 10-mile TT, a feat I doubt I'll ever replicate.