NOWADAYS, warming up a WhatsApp account does not mean anything at all whatsoever (those days are gone).
A WhatsApp account gets suspended automatically (nowadays), if even a few people report it for spamming. And nowadays, such suspensions by WhatsApp, are permanent.
Hence, you can warm up a WhatsApp account even 1 or 2 years, but the moment a few people report it for spamming, then nowadays, such a WhatsApp account gets suspended automatically and nowadays, such suspensions by WhatsApp, are permanent. Therefore, nowadays, warming up a WhatsApp account does not mean anything at all whatsoever.
Ofcourse, apart from spamming, (nowadays) there are also plenty other reasons for which WhatsApp suspends accounts, no matter if such WhatsApp accounts are aged, no matter if such WhatsApp accounts are warmed up.