One could say the same right now for Sotomayor and Kagan in their mid to late 60s. If Biden put in 2 40-year-olds right now there wouldn't be much chance of them being replaced during the next few administrations.
It's Democratic political malpractice.
Almost as bad as forcing a deeply unpopular presidential candidate because of a lifetime of political favors and all the corrupt money in the world. (Or the Blue 'Murican half, at least)