A petstore that sells piggies was located just down a strip mall by Kay's in my area (I was going for a mother's day gift). I stopped in to look at the piggie supplies and went to pet the piggies ( I cannot resist petting them even though they are in a petstore) and I pretty much was teaching myself how to sex a piggy while I was there. I was picking randomly ones up (they were not separated by sexes which is a BAD idea from the stores part obviously) but I ignored it (took all my might to) and was teaching myself. I found a really friendly little thing, did not squirm at all, and it was comfortable in my hands. Didn't try to get away, was very nosy with my rings I had, and I thought "Oh, what a sweetie!" I checked the sex, and you could def. tell it was a HE!!!! Had he been a girl and in a shelter I would have taken him home in a heartbeat. Most calm piggy I'd ever come across, especially for a petstore when all hands are reaching down and picking them up.
He was probably about 8 weeks I am guessing??? My friend went in and actually asked about them and she was told they were 4 weeks (another reason I refuse to buy a piggy from a petstore now to profit them taking little ones so early).
I think you can type in google about sexing piggies, and I also have learned that way. There for a while I thought my Little Red was actually a male because she kept trying to mount Mocha for like a week so I was OCD about checking her and Mocha and comparing. Little Red is most def a girl and so is Mocha. Little Red was just hitting a horomone spike from what I understood.
I keep rambling! Sorry! I never have understood they Y concept honestly...Good luck to you!