Authorizing my MacBook Air but says I have 5 devices authorized; I only have 4.

Note that only computers (not iPhones or iPads) are authorized devices.

Deauthorize all and then authorize any computers you still have and want to use. See the following from Authorize or deauthorize your computer for iTunes Store purchases - Apple Support

To deauthorize a computer that you don't have access to, you have to deauthorize all of your computers. Then authorize each computer that you have again. You can deauthorize all computers only once a year.

1. Open iTunes.
2. Choose Account > View My Account.
3. Sign in with your Apple ID and password. Forgot your Apple ID?
4. At the top of your Account Information page, go to the Apple ID Summary section.
5. Next to Computer Authorizations, click Deauthorize All.
6. Authorize each computer that you use again.

Also note that there is a difference between authorized and associated devices -- see: Authorization vs. association - Apple Community