The Christian objection I've heard is that great longevity means putting off going to Heaven. I've never heard a Christian say that great longevity increases the odds of repenting and avoiding Hell.

During a long life a Christian may repent many times, and sin again many times. Whether they go to Heaven or Hell depends on when they die. Suicide is a mortal sin because otherwise they'd kill themselves after repenting. So they do the next best thing, and repent when they think they're going to die. Confession and absolution on a deathbed are standard. Conversion and baptism on a deathbed are known to happen.