Do runners improve with age?

Iam asking this as I sit waiting for my birthday to arrive in 2 hours time. Would.'t it be nice if that was the case. In my eyes, the main thing is not to get any worse at the very least. I was feeling a little 'off' to say the least before I went for my run this evening with the boss. I don't think he likes excuses normally but he and his good lady had experienced the same thing yesterday so a bit of sympathy seemed to show up. Very welcome as the first couple of miles were hard. Then as we turned down a woody off road path (really a short cut rather than running the full 6 miles)Iseemed to find my stride and enjoyed the last mile. That is around 14 k so far if the week starts on Sunday but knees are a bit tender so not sure how much more I can do this week. Let's see shall we....! HAPPY BIRTHDAY TO ME(: