Yes, but you would need to replace it with a different one. That is an Apple account cannot be left without an associated email address.
click here ➜ Change your Apple Account primary email address - Apple Support
Once changed you will need to wait at least 30 days before the email address can be re-used according the support document linked above this line.
You can request the Apple account be terminated entirely instead and that will also eventually release the email address but it won't be usable for another Apple account for several years according to the support document linked below this line.
click here ➜ How to delete your Apple Account - Apple Support
For both operations you need to know the Apple Account's password and have access to the account.
Do note, all purchases and data linked to apple Account will be unavailable if you choose to delete it. So make sure you and your son, don't have or need any media or apps that are tied to that Apple account before deleting it. Also, make sure no devices are still linked to the account as once deleted the devices may be unusable.