You will need to check with state laws to determine the legal age, but federal law says the legal age to sign a contract is 18.

Typically, the signer of any contract must be 18 or over (not a legal minority). There are some situations where a seller will waive this right. So will let a 16 year old sign a contract but it is not legally binding.

You can typically sign with a co-signer, but they are the responsible party and you still need legal guardian approval.

The same applies for an insurance contract.