Life span can be easily translated into standardized units more convenient to talk about which the breeder's equation would apply to, the same way binary or cat

Life span can be easily translated into standardized units more convenient to talk about which the breeder's equation would apply to, the same way binary or categorical or polytomous traits can often be treated as a normal latent with thresholds. And people calculate heritability of lifespan all the time. (It's low, but that's not because lifespan happens to be Gompertz-distributed.)