Need advice for starting my real estate

If I were you I would hand the property right back to my parents and ask them to give you some time to grow up before they burden you like that. Anyone who thinks the economic benefits of a choice like this for you outweigh the risks needs to think this through.

A quadplex that grosses $2,500 a month and is free and clear ends up being some variation of four apartments that each go for $625/month. Not a single one of my own properties goes for that much. Just so we can at least try to compare apples to apples here, the median home sales price in Pittsburgh (where I live and operate) is $242,000. The median home price in Houston, on the other hand, is $320,000. I think the most obvious assumption is that we're talking about a solid D property.

Your parents may have the hard-won skills, the deep pockets, the landlord-life experiences to make a D-class quadplex work. There's no reasonable way you do. The most likely outcome is that, eventually, this place will bankrupt you. I've seen places like this bankrupt people twenty years older than you, who have been plenty successful in other areas of their life.

Give the quadplex back to your parents and ask them what books they think you should read, what you should study in the next few years, where you might want to go to college.

I would add to my advice that you should start reading about personal finance and how  real people actually get rich. You'll find there are very, very few 16-year-olds that have been handed rental properties like this and have gone on to meaningful lives of prosperity and happiness. Life's just not that simple.

I really hope this is all a tall tale, an exercise in make-believe for you, and your parents aren't really making this choice. I feel deeply sorry for all of you if you're telling the truth.