Milks are not known for canabalism like most kings. A 3.5' male should be fine with a 5' female. Just keep an eye on them for the first few minutes to see how they react to one another. The only problem I could see is the male just not being mature enough, but I doubt that would be the case. I say go for it. Be sure to feed your female frequently....your male will probably lose interest in food while breeding. Good luck.