How old do you have to be to buy land/a house?

St Louis home buyers from https://bitly.com/3dYDoxE

18 in California. Old enough to sign contracts. 

you can't assemble a condo on a house. most drafting laws won't permit the house to be destroyed and lofts fabricate, now and again you can't set up a 2-4 family house in it's place.

A 16yr old can't sign a legal contract that would stand up in court, so on their own without an adult signing and taking on all the legal responsibility ( and rights) no it is not possible

You cannot legally have a contract with a  minor--someone under the legal age of 18--without a legal adult being on the contract. That would include a home purchase or land purchase. If the minor is legally "emancipated", i.e., considered by the court as a legal adult, that's different. 

A 16-year old may indeed have the money to buy a house, but some legal guardian or payee has to sign that contract. It sounds to me like your 16 year old is yanking your chain. 

As far as a business, that's a little different. A 16-year old can own or start a business. There aren't any contracts involved in doing that--BUT--if the business does something illegal or fraudulent, or if they cheat a customer and the customer decides to pursue legal action against the business, then they won't be able to sue the minor--only the business. There are some tricky rules here. 

A 16-year old can, in fact, buy property anywhere in the US providing:

a) they are fully emancipated by a court, OR

b) their parent/legal guardian signs for them.

It is the same if they "own" a business. They may be a shareholder, but the owners of the business are the ones who are ultimately responsible.

Someone who is not of legal age cannot legally sign a contract.

Construction companies will not sign any contract with a minor - because of the law, the minor does not have to fulfill their side of a contract (paying the bill)

Also, the land that he would own may not be zoned for an apartment complex. 

In any case, the minor would need several hundred thousand dollars to build the infrastructure and such.

"I had a 16 year old come up to me today and said that he was going to buy a house and that he was going to build an apartment community on it."

I'll take 'things that didn't really happen," for $500, Alex. 

You have to be of age as an adult to complete a contract. 

You have to be an adult to enter into a contract. As he is clearly a minor he cannot personally buy land or a house.

He is delusional or you are a troll.