Unarmored defense and tortles

just as a question for all dms what is your ruling on unarmored defense and tortles natural armor. I had a charecter concept as a tortle barbarian wih a theoretical ac of 21 at level one (10+4 con+7 natural armor) so how woould you go about this

yeah Nah.

Rules for AC say you choose on method of calculating it so you choose between the two options you have.

Barbarian = While you aren’t wearing any armor, your base Armor Class equals 10 plus your Dexterity and Constitution modifiers. You can use a Shield and still gain this benefit.

Tortle = Your shell provides you a base AC of 17 (your Dexterity modifier doesn’t affect this number). You can’t wear light, medium, or heavy armor, but if you are using a shield, you can apply the shield’s bonus as normal.

It is either 10+4 con+? Dex

or 

10+7 natural armor