So longevity escape velocity is defined as adding more than one year of life expectancy per year that goes by. That is on a population level. That doesn't necessarily mean every individual in a population is biologically immortal.

Take Ray Kurzweil for example. He's already 74. Even if we add more than 1 year per year for the population in 2030, that doesn't mean Ray personally will achieve LEV. He'd be in his 80s at that point, and will have a much higher per year risk for developing cancer or dementia than someone who is 25. Someone who is 25 may have reached LEV, but someone who is 80 perhaps hasn't.

It's complex maths to solve for the actual risks and probabilities, but you can just use logic to reason thru this.