I was ruminating more on this:
I still think you should list it, but definitely be ready for questions about it. Not to imply anything in your case, but if a 19 year old comes up to me telling me he owns a business, I (and adcoms likely too) are going to have some questions - because it's unusual.
I'd find it hard to believe, for example, that in high school you went out and found a bunch of investors or raised the money working as a lifeguard to open up a Subway franchise. Again, not implying that you didn't - it's just that it's unusual that you could. So if it's the kind of thing where you "own" it as a gift from your dad or something, I'd undersell your position rather than overstate.
But again, it's quite possible that you really own this building and would have great answers for all my questions, in which case it's a win-win-win writing it down.