Here are better pictures of one leaf, for the size.
Ynk88, your seedling has unique shaped leaves. I think it's not a pure pummelo, but some sort of pummelo hybrid. Some pummelo hybrids still have heart-shaped petioles.
This is one of my pummelo x Ponderosa lemon hybrid seedlings. The petioles aren't as big as these on your plant, but some of them overlap the leaf in a similar way.
And this one has elongated leaves, quite similar to yours, but petioles are smaller and rounded.
If yet another combination had happened, a seedling from this cross could have both overlapping petioles and elongated leaves. Then, I think it would be quite similar to yours.
I'm not saying your seedling is exactly a pummelo x Ponderosa, but who knows.
@edit: changed hosting. Photobucket doesn't work properly.