How Does This Pass the Article Three Muster?

For the first 100 and 30 years of the federal a judiciary, you had federal judges. And then all of a sudden, about a hundred years ago, congress is like, no, we want senior judges. All the old judges can go into semi retirement, and maybe they'll work only a quarter of the time. The second thing is, constitution is whatever five dudes and robes say it is. So what's to say that anything is unconstitutional these days?