How old do you have to be to lease out a retail space ?

For the most part, there is nothing illegal about entering into a contract with a minor.  However, the question is whether the landlord will do it, and the answer is probably not.  In general, contracts with minors are voidable at the option of the minor.  There is no upside to the landlord signing a contract (a lease) with you which you can void if you want, but which it will be bound by if it turns out to be advantageous to you.  Also, a landlord will want a security deposit and assurances that you are able to pay the rent.  At age 17, it is doubtful that you have built up a credit rating and/or have amassed sufficient assets to provide the landlord with the security it will want.  In most, if not all, states (I'm not sure about New Jersey specifically), you will legally be an adult, and bound by contracts, when you become 18.