Becoming an E-1 at age 40 isn't a "career path", it's a last resort for somebody who for whatever reason can't make more than $30K/year with the skills they've gained over the last 25 years, and for whom having functioning knees is less important than needing the money.

So they should just age out in poverty and die? Such people exist. To be clear, I'm 1000% against anything resembling a draft, but if an older person wants to, why stop them? A guy in my brother's medical doctor graduation class was 46 years old. Good thing nobody explained to him it was too late and he failed already.

In all seriousness, I do agree about the functioning knees part. But as long as it's voluntary, I don't see the downside.

They had 40 years of functioning knees, but it didn't get them to a place where army wages or army housing looks good. If the army breaks their knees, maybe they can get service related disability.