Is level 6, 23 AC without magic items possible? I have an early DotMM campaign I'm playing in, and one of the other players is using an insanely high AC to just run around and kill everything, regardless of other players.  I'm fairly sure he's increased his AC without the DM noticing, but I don't want to call him out on it without being sure.  The character is min/maxed around increasing AC as much as possible.

He's an aasimar warlock 1/paladin 5, with a ring of protection.  He uses a shield, and what I'm assuming is splint armor.  He claims his base AC is 24, letting him get up to 26 with shield of faith.