A 50% mortality rate per year translates into there being a <0.1% chance of living for 10 years. How does that translate into there being "no limit to longevity?" I seriously don't get the claim.
Once you get to 117 years old, there are only a few people worldwide that can be used to determine that survival rate, and those people are already subject to a selection bias of people that are exceedingly long-lived.