Armchair graphene nanoribbons (aGNR) are promising as a host material for electron spin qubits because of their potential for scalability and long coherence times. The spin lifetime T1 is limited by spin relaxation, where the Zeeman energy is absorbed by lattice vibrations, mediated by spin-orbit and electron-phonon coupling. We have calculated T1 by treating all couplings analytically and find that T1 can be in the range of seconds for several reasons: (i) Van Vleck cancellation; (ii) weak spin-orbit coupling; (iii) low phonon density; (iv) vanishing coupling to out-of-plane modes due to the electronic structure of the aGNR. Owing to the vanishing nuclear spin of 12C, T1 is a good measure for overall coherence. These results and recent advances in the controlled production of graphene nanoribbons make this system interesting for classical and quantum spintronics applications.