You have to look at the bigger picture here, you'd be sacrificing a lot more on your end by sticking around with her, than her giving up anything...Older women get that, especially about younger men.
You don't have to mention her age, but hint that your wants and needs in life are different and may not align with hers. And don't feel bad or guilty or selfish or whatever for breaking up, you went head on into something with high hopes, only to find out it wasn't for you.
And if you haven't slept with her yet, and gotten close, be careful, sex could be just that thing, the carrot she is dangling over your head, and will feed it to you, as soon as she detects you slipping away from her. And chances are good that sex with this woman will be like a Lay's potato chips. You can't just have one, (it will be amazing) so... bare that in mind, and refuse, turn it down and walk away. You have to let your brains do the thinking here and not your heart.
I don't know her, nor will I make judgements, but women at that age, with kids etc. Know a thing or two about starting a family and keeping it. If you catch my drift, you need to end this as delicately and as soon as possible, If you know this is not what you want as a partner for the long run. Break up with her if you feel it's the right move....Most importantly don't feel Half assed and guilty doing it. She'll be fine.
*I don't know why I mentioned her with Kids, I don't think you said anything about her having kids, my bad, scratch that part.