I don't think it will extend lifespan past the benefits you would get from a good diet + exercise + weight loss...but thats still significant. Its more about quality of life... through improved body composition, less abdominal fat (which decreases cardiovascular risks), mood elevation, supporting mental function, promoting recooperation from injuries and basic wear & tear, holding more water in skin & muscle is good for older people, small increases of organ size & function (organs actually shrink a bit with aging), & small increase in bone mass (battling osteoporosis). When all of this is examined in the context of an older person (ie 50s and beyond), there are significant benefits for those that are deficient.
insulin and anabolic steroids are much more anabolic to the tissues compared to GH. I stand by my opinion that GH is a basically a waste of $ for athletic performance. It causes a small amount of muscle growth but BBing doses maximizing this effect still don't give a bang for the increase in side effects or cost. Bottom line, don't use it for sports.