As a very broad generality, steel (or Ti) frames will outlast an aluminum frame since they aren't subject to a finite fatigue life while aluminum is. That said, the fatigue life of a durably built, not ultra light, aluminum frame could be many decades but a steel frame protected from rust damage can be an heirloom.

At your weight don't even think of an ultra light boutique steel (or aluminum) frame. Surly's Disc Trucker should last indefinitely since it's intended to carry the rider and who knows how much luggage weight over long touring distances.