How long should notification be stored in a system

Hye,

I'm designing a management tool for admin and an app for user they managed.

I'm not sure of how long should the notification be stored before expiry? In the app, I suggest to use a 30-day interval, so notification will no longer show up in the notification list after 30 days. This is due to the fact that many activities has been resolved after 30 days.

I'm having issue with the management tool for admin since its a one-account-for-all-admin, they will receive much higher volume of notification compared to the individual user in mobile app.

Should the admin tool notification follows the 30 day convention or change to something like after 100 notification, it will no longer displayed?

Thanks in advance!