altho we are never told the average life span of a kajiit i don't think it is that long (unless he is on like his 5th out of 9 lives)
so i concluded that he is probably a deadric prince that bethesda put in there and never told us.
i have read the discriptions of the deadra princes and the one that fits the lying aspect is Boethiah
Boethiah is the Prince of Plots, who rules over DECEIT, conspiracy, secret plots of murder, assassination, treason, and unlawful overthrow of authority. He is depicted as a great caped warrior, often in a stoic pose. He is one of the original ancestor gods of the Dunmer.
Boethiah loves competition and battle, and this nature is manifested in his quest in Oblivion,[2] transporting the player to his realm of Oblivion for a tournament to decide who is truly worthy of Goldbrand, an enchanted katana with a gold-colored blade (rebuilding his shrine near Khartag Point in Vvardenfell is enough to claim the blade in Morrowind).[1] He is occasionally known as Boethia, a feminine Persona, and the infamous Pillow Book is named in his honor.
Deceit can be taken as lies.
So in conclusion M'aiq the liar is really an aspect of Boethiah.