Been an on and off runner for about the last 15 years. Although I got reasonably fit before, and have completed 2 marathons I've never been disciplined enough to really train often enough or consistently enough. Turned 40 last October and decided that with my previous best of 40:44 for 10k it was time to beat the 40 min barrier. Started running last November after not doing much for a couple of years, and nothing for 6 months.
Took a while to build up, but eventually realised the only way it works for me is to go early morning - been running on ave 6 times a week since Feb. 10k in Jan, did 46 mins (big hill), In April 42:25. Completed a spur of the moment half mara in July in 1:33, and did a park run last month in 19:14, which predicts a 39:59 10k according to Mcmillan. Now I've just got to find the right race to bag it.
In my experience, no, you are not too old. Ed Whitlock ran under 40 mins for 10k to set the 75-79 age group record!!!!!