I think that age is fine... But unless it's absolutely necessary I wouldn't take the risk, they can die under anesthesia or from complications during surgery, infections post-op, ect. But I'm a worry wart and a mother hen so. :I
The thing is, if I dont neuter them I probably cant keep them, because their dad was very agressive at the age of one, bit a GIANT hole (5 cm) on the owner that had him since day 0, 3 rats form the same litter as the dad were agressive, and another rat from the same dad that the dad comes from, but from a different litter was agressive too, there is allot of agression in their family and I'm not willing to risk such a thing happening.