Let me answer your last question first....
The price of having a female would probably be her death at the hands (or fins) of the male.
In a tank that small a female would be dead within a few days if not sooner.
The male having had this tank to himself all these years and then suddenly having a tankmate would not take kindly to it.
I have known breeders (myself included) who have breed these in a 50 gallon breeder tank (36" x 18" x 18") at a young age and when not fully grown. Even then a partition was used to keep the two apart as the male wanted only to kill the female.
It is not wise to try breeding this fish in anything less than a 6ft tank IMO.
As for the age of the fish. Age is really only a factor on egg production. I have not read any studies on whether or not age has a bearing on a higher rate of deformities or not.
As for the striped midas...this is their natural color form and would probably produce fry of several color varieties.
HTH