Let me give you my example, which might be more reasonable. I'm 25 years old. I started running when I started high school 11 years ago in 2000. At the time, I was the worst runner on the team, not counting kids who ran for a week and quit the team. By the end of high school, I was one the better runners on the team.
My times, apologies for the odd cross country distances in Ontario:
2000 - 27:54 5k
2001 - 31:18 6k
2002 - 28:20 6k
2003 - 30:xx 7k
2004 - 18:45 5k, 40:30 5k
2005 - 18:29 5k, 38:52 10k
2006 - 18:56 5k, 38:40 10k
2007 - 17:44 5k, 36:38 10k
2008 - 1:21 half marathon
Since then, I've been busy working and haven't quite gotten in the training (about 80-100k a week) to run faster than those times. If I'd continued the progression, I might be running 33-34 minutes by now.
My ultimate goal remains a sub-2:30 marathon (my high school coach ran 2:30, but never under). I'm not sure if I'll get there, but there's nothing to be ashamed of if you run even under 35 minutes for 10k or 2:50 for a marathon.