The promise that Jesus made to His disciples that more than likely doesn't refer to the Millennial Age but to the Perfect Age; the Age that will follow the remaking of the New Earth by Fire.

"And Jesus said unto them, Verily I say unto you, That ye which have followed me, in the regeneration when the Son of man shall sit in the throne of his glory, ye also shall sit upon twelve thrones, judging the twelve tribes of Israel."