One has a total powered-on time of 51534 hours, and the other 49499 hours.
As for their actual age (manufacturing date), the only way to know is to look at the sticker on the drive, or find the invoice, can’t tell you right now.

$ for i in /dev/disk/by-id/ata-WD*; do sudo smartctl --all $i | grep Power_On_Hours; done
  9 Power_On_Hours          0x0032   030   030   000    Old_age   Always       -       51534
  9 Power_On_Hours          0x0032   033   033   000    Old_age   Always       -       49499

Follow the official documentation, nothing else comes close.

I have automated this process in my nextcloud ansible role

• simple: rsyslog: all local logs to a central syslog file (using the imfile module), all syslogsfrom all server to a central rsyslog server (over TCP/SSL, example here). Use lnav or something similar to consume the logs
• more complex, resource-heavy: Graylog Open as a replacement for the central rsyslog server, setup pipelines/alerts/whatever… Currently considering replacing my Graylog instance with Wazuh but I don’t know yet if it will be able to replace it completely for me