Shoggoth's being a Lovecraftian horror, they are ageless and thus, do not die of old age.

Shoggoth are almost always are on the Chaotic side and are nearly always Evil, Lawful Good Shoggoth's are unheard of.

You can see 120ft in the dark as if it were dim light.

You gain proficiency in Intimidation and one other skill that requires Charisma

You follow Shub-Niggurath giving you 1 Cantrip from any class to use as you wish, with Charisma as your spellcasting mod.

You must have a mask on (you pick how it looks) if you enter a town or you will be attacked by who ever sees you. You start out with this in your inventory and a cloak to cover the rest of your human shifted body. The cloak can only be on if you have no armor, chain mail, or leather on. 

At 5th level as an action you can turn into your natural state. In this state you can see 360° around you in any direction, your movement speed is 40ft and you gain Bite (3D6+Strength mod Piercing). You can not cast your cantrips or spells in this state.

You take 5 hours instead of 8 for a long sleep and gain all the same benefits.

You have a total of +4 to spread around any of your rolls and a -1 to your Dex.

The Shoggoth is ancient, you know Common, Under-common, Deep Speech, Abyssal

Shoggoths being so horrid must hide their true form, this altered form is the size of most humans, being 4-6 feet tall. Your size is Medium.

The shoggoth can breathe air and water.

When you go unconscious you lose your hidden form and attack the 2 nearest creatures within 60 ft of you on your the first turn before you make your saving throw.