Is slavery still permissible and what are the conditions for marriage?

Is concubinage and slavery abolished and abrogated? 

Are the only conditions for marriage today still puberty and mental maturity? 

I’ve seen sunnis say slavery is still permissible as war booty and they use the Prophet’s, peace and blessings be upon him and his progeny, marriage to Aisha to justify marrying girls under 18 today if they hit puberty, is this correct?