Re: im trying to change my old email address on my apple id but my new valid email address says its not available
Maybe that address is in use already, by another family member's Apple Account.
You can check if there's an outage: Apple - Support - System Status (A green dot = All ok)
Else: Wondering which Computer or device you use, and which OS version is installed:
(Eg: May need latest OS version for that model : if updating is always wise to back-up first)
Also wondering where you tried to change the email address :
(Eg: In the device or computer / using iCloud / logged into online Apple Account)
_________________________
If you haven't seen it already: Apple support's online article may be helpful:
See: How to: Change your Apple Account primary email address - Apple Support
Restarting a computer or device will often restore order if something is not working as expected.
(Eg: deletes temporary files, re-establishes connections, may updater recent setting changes etc., and more)
_________
If needed : Apple Account Support Website (info. / support / contact options etc.)
Apple Account - Official Apple Support