Well according to my Chinese horoscope, my best matches are in multiples of 4 years older or younger than I am. So I think the oldest/youngest I will go from my age would be +/- 8 yrs.
Older: Up to 13 years, n.b. only if they could keep up with me and looked younger. Younger: A few years, but they'd have to at least be at the same level of maturity.