Really? I thought you were quite a seasoned runner, I was running 22s when I was taking it fairly seriously and I was never especially talented. You should be able to hit 25 with a bit of training, just have to take 30 seconds off at a time. Do you do any kind of fartleks or interval training?
I've got no natural ability either, it's just about doing the graft. I've tried to do something every day (mostly running/rowing) since December 2nd after the Belvoir 35 Minute Horror Show and I've missed only 4 days. Since throwing in hill repeats and some fartleks my times have started to come down.
The fact that I've no idea what fartleks are is likely my problem. I've never done any sort of training schedule for my running. I just go out 1-2 times a week and do whatever distance I feel up to doing. Well, other than in the run-up for an event, when I do follow a vague plan of increasing distances.