Age
I am 57, and I asked my surgeon the same question. As I recall, he told me that they don't start worrying about age until 70, and then they consider WLS on a case-by-case basis.
I had VSG this past Monday, and it went very smoothly. The nurses were impressed at how soon I was up and walking, and at my walking speed. From what I've read, there's no reason to believe your age will make your recovery more difficult. It has more to do with how anesthesia and the other drugs affect you.
I'll turn 58 later this month, so we are pretty close in age.