(Houston, TX, U.S.A.)
Bought on eBay. Desc was Larger-Agave-unsure-of-name-Awsome-teeth-cactus-succulent-not-aloe.
Yup, that's an Agave alright. The dead giveaway is the wicked spines at the tip of each leaf, and the nasty armament all along the edges. Unfortunately, there is no way to positively identify a young plant as they haven't started showing their true characteristics.
Those are pretty distinctive teeth though, so it's possible you could narrow it down using that descriptor in a search. Look at these to see if it's similar;
Big Bend Century Plant
Cows Horn Agave
Whales Tongue Agave
As there are so many, it's very difficult to pin them down, because not only do they appear different when mature than as juvenile plants, they also appear different when grown in other conditions.
These are long lived plants, hence the name, Century Plant, so you'll a lot of time to discover it's real identity as it reveals it's true nature.