Electrolytic capacitors are the default reason a component made today would only last "20 years" or so. BUT those should be readily replaceable for a renewed service life, unless there’s something weird about the component design to make this much more challenging than usual.
I have a hard time believing a properly designed preamp would only be "good" for 20 years. It should outlast most of us here. I’ve owned PS Audio components in the past, with no problems so far. There is nothing that indicates to me they’re not properly designed for good longevity.
The BHK amps might throw around more heat than average, but 20 years still seems absurdly low for a preamp. It reeks of misinformation.