For how long should I keep backups ln Time Machine for my MacBook Air?

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For how long should I keep backups ln Time Machine for my MacBook Air?

Best to let Time Machine handle that. In trying to selectively delete certain backups, you may give Time Machine a case of amnesia.

See the descriptions here:

Back up your Mac with Time Machine - Apple Support

It says TM will auto-delete the oldest backups when the drive gets full.

I can give you an example of how far back TM can go from my iMac. I have a 1TB factory SSD, and the Time Machine drive is a 2TB fast mechanical hard drive in a USB3 enclosure. The Mac went in service around the first of November 2018 and I've never deleted a backup. The oldest backup shows April 2019, which corresponds with when I replaces the old and slower 1T TM backup drive with the 2TB. There is still over 400GB free on the current TM drive. That's 4+ years, so no need to delete anything in my case.

Although the recommended minimum external drive for TM is twice the capacity of your internal drive, I have used smaller drives and still had 2-3 years of files available.

You can, however, save TM space without having to delete. Go to Settings > Time Machine > "Options..." button and eliminate things you know you will not need to search:

In this example, the drive "Clone Car" is a secondary backup made with Carbon Copy Cloner that stores a bootable copy of my SSD to a separate drive every morning at 4AM. I see no reason to back up another backup that can never be over 24 hours old. Eliminating that device saves half a GB of space and speeds up hourly TM backups.

Remember— the first TM backup will be the slowest, having to back up everything. Incremental backups are fast because they only have to update files that have been changed since the previous backup