To get a Mametchi on a V4 you need to get ur smart(pencil) points up to 100+ before it turns into an adult. But it will only work if you have either a young androotchi, ringotchi, young mameitchi, or young mimitchi as a teenager.
To get a Mametchi, have a boy Tamagotchi, hope that it becomes either a Yangu/Young Mametchi or a Yangu Robotchi/Young Androtchi, then increase its intelligence (pencil) points so that it's higher than its style or kindness points. It doesn't have to be that high, as long as you have enough skill points and have given decent care to prevent your Tamagotchi from becoming a universal Tamagotchi, you should still get Mametchi.