How old should a male rat be before the testicles start showing?

I got a pet rat from Petco a few weeks back. My cousin got one the other day. Her rat and my rat are definitely males but hers is older. Enough were her rats testicles are prominent. My rat's are not. He's a young rat so I am wondering, when should his testicles be prominent?

He is a she! Male rats testes become apparent at about 3-4 weeks. Petco doesn't start selling them until 4, and you got your gal a few weeks back, so it's a she! If you are unsure, look for nipples, which only females have.

Curious to see your rat's underside now.Can we get a pic?Yes, I realize this is not an answer.Sorry.

i have a litter of rats which are 4 weeks and their testicles are now showing (really prominently)so if your rat is older than this (which it should be if you have just bought it - rats shouldnt be sold under the age of 6 weeks, 5 weeks at a push) it should have his testicles showing by nowIf not, he is a she! This happened to me, only i got mine from a breeder which should have been more reliable! And hence the litter i have! lolGood luck! If you have another rat which is definitely a boy, make sure you keep this female in a different cage as you will end up with babies like me! If you dont have another rat, please consider getting one! (a same sex one - look up how to sex them on the net and check yourself when you go to pick up ratty) Your ratty will be much more happy and healthy :)All the best