I believe selected humans or hybrids (we are all basically hybrids)may live for centuries.
Appearing over spans of time to an ignorant populace,this seems to be "Life Everlasting" and I might add good health.
Nobody lives forever but the Visitors are so advanced they can extend your life. But there are other factors.Diet for instance. You would not be allowed to eat meat or solids. Notice the hybrids are all very lean.
Jesus for instance. When he first reappeared after the Ascencion,he was unrecognizable (probably devoid of hair) and said that he was hungry.
One example.