I rent a home (4b4/3 ba) and the owner has hired a new property manager. The new property manager is requiring that all adults in the house sign the rental lease. My son is an 18 year old high school student, headed for college in a few months, and I have expressed that I will not allow him to sign a legal document, especially a long term lease for a home that he could never afford. The property management company's policy is that all adults sign the lease, and they won't budge or grant a waiver. Do I have any options here other than moving? I am in the state of California.

Not really anything you can do... Its their right as the property owner and they do this to cover their own interests. And yes they can require all adults living in the residence to sign the lease. And refuse to rent to anyone who won't sign it.

Your son would only be held liable on the lease if you failed to pay. Are you planning to not pay or become late paying this year?