He may be 40 but he's only ever lost one season to injury and on a fluke hit. The guy is like a DUI driver walking away from a flaming wreck. He goes limp noodle every time he gets hit, and it's not accidental he counts on getting hit and knows how to react to it. Plus it's not like Garoppolo was bad when he played last year. Also a weak division and likely a high playoff seed. Their odds are hard to discount.
Steelers are so loaded offensively it's ridiculous but Ben is not great on the road. They lose too many games that they shouldn't, he takes too many hits on his legs (and their backups are awful). I predict they go into the playoffs with a a 3 seed, lower seed than they probably should but Oakland will beat them out for the #2. But if Ben, Bell, and Brown (Bryant as well) are all there they would be very tough to beat.
Seattle just nabbed another top flight defensive player for this year. If all he does is put a choker leash on Bennett to keep him from jumping off-sides every third play he will already improve that defense. Really though, if they stay healthy they are going to be really good. I personally think Lacy will be a bust, another overrated SEC/Alabama player but both Rawls and Procice are good enough to produce a decent running game. Seattle has the easiest division in the NFL without a doubt so playoffs are a given it's about staying healthy.