Tell me about aging...

Hi, First time I am posting here, I used to lurk in the Boomers on CR every once in a while. I am kind of upset at my poor training run times these days. I cannot decide whether it's the cold, New England weather, or if it's my age that is starting to show (I am turning 48 next week). But I am training for Boston and have more aches and pains than I can ever remember. And it's marathon #35. No injuries, thank goodness. I have really never had a running injury in 20 years of running. But I am upset about it, I admit. I have never been out there taking so many walking breaks and being disappointed at myself for taking them. Any words of wisdom or anything to share?<br>
(I hope this is not arrogant; definitely not meant to be.)