Thanks for the responses so far guys.
I didn't mention the specific marathon because the running community is small and there is enough information here to figure out who it is if you knew the city. It is a legit city marathon that is run every year. I know there's no way she even knows Letsrun exists or posts here. She doesn't really use the internet or social media.
Troll accusations actually make me feel better because that means this sounds ridiculous.
I don't think she would talk about her running that much because it's not her first athletic accomplishment like most people who start training for marathons (she was a collegiate champion in soccer) so it's less the volume of conversation and more just not knowing things that I would think would be normal to know about training, but maybe this group just isn't very well coached.
So four days a week sounds legitimate? I guess I can call the store back and ask how often they train I didn't think about that when I called the first time. I can't call until I finish my next class and they'll be closed by then so I'll try tomorrow.
I did offer to get her a watch back when she started but she has always made fun of mine and said she didn't want to wear a computer on her wrist so that's out, but now I'm a little more suspicious of that too.
As for dating an older woman, I've found that they're much easier to get along with because they're more mature. And until recently had a way higher sex drive than most women my age, too. The difference isn't that much anyway (5 years).