Well, it's kinda creepy. I've always like the 20% age range scale, because it keeps you both in the same area of life and such.
An 18 year old should be looking for a uni degree, or a career, and will probably need to move around. A 26 year old has probably got those things already going on, and likely is in a different stage in her life. One of you will eventually have to give up something for the other one.
But yes, if I was her friend, I would see you as the creepy older woman who is leeching off her youth, so to speak, and I would be wondering if it was a bit exploitative. But then, in China, I see a lot of it and I've learnt to stop questioning because they like age gaps in their partnerships.
So I suppose "shrug and don't be surprised when you want to settle and she still hasn't lived, leading to a painful break up."