Good luck finding anyone willing to issue you a cert that's valid for 20 years.
But I wasn't talking about leaf certificates, I expressly mentioned this for the CN in _root_ certificates and it's pretty common for those to have a lifetime of ten, fifteen even twenty five years.
Here's an easy to remember example, https://crt.sh/?id=1 the first entry in the crt.sh database.
The Common Name on that certificate is "AddTrust External CA Root". So... who are AddTrust? I actually have no idea. This root is today controlled by Comodo, a CA in the United Kingdom but you'd never guess that from the certificate.