I just read that I cannot amend my return to include the American Opportunity credit if I am past the deadline. I forgot to claim the credit for 2016. Is this true?

No it is not true.  You have up to three years from the filing deadline to submit an amended return.

If you need to enter additional information, delete something, or change something on the the tax return you already filed, you have to wait until your return has been fully processed, then you can prepare an amended return, called a 1040X.  You cannot e-file a 1040X.  It must be printed, signed and mailed to the IRS.

https://ttlc.intuit.com/questions/3061514-how-do-i-amend-a-2016-return-in-turbotax 

After you print, sign and mail your amended return—1040X— to the IRS wait about 3 weeks and then you can begin checking on it at the IRS website.  Be aware that it can take at least 3-4 months for an amended return to be fully processed (or sometimes even longer.)

https://www.irs.gov/Filing/Individuals/Amended-Returns-(Form-1040-X)/Wheres-My-Amended-Return-1

https://www.irs.gov/filing/individuals/amended-returns-form-1040-x/amended-return-frequently-asked-questions

You are allowed to amend to claim  and educational credit. But there are other restrictions. For example you cannot be a dependent or even be eligible to be a dependent. Furthermore, A student, under age 24, is only eligible for the refundable portion of the American Opportunity Credit if he supports himself by working. You cannot be supporting yourself on parental support, 529 plans or student loans & grants. You must have actually paid tuition, not had it paid by scholarships & grants.  It is usually best if the parent claims that credit.  
For full rules, see <a rel="nofollow" target="_blank" href="https://www.irs.gov/Individuals/AOTC">https://www.irs.gov/Individuals/AOTC</a>

Thank you, I am a parent so I meet the requirements. What I read was regarding not having SSN by deadline so I read it wrong. I am relieved.

That throws more light on your problem. Retroactive claims are no longer allowed for earned income credit (EIC), child tax credit (CTC) or American Opportunity Tax Credit (AOC) for any taxable year for which the taxpayer has a taxpayer identification number that has been issued after the due date for filing the return for such taxable year. That is, a taxpayer who files a return with an ITIN and later receives a SSN may not amend prior year return to claim EIC or amend a prior year return to claim CTC or AOC for a dependent who later received an ITIN or SSN.
reference:  <a rel="nofollow" target="_blank" href="http://www.thetaxadviser.com/newsletters/2016/jan/congress-makes-changes-to-popular-tax-credits.html">http://www.thetaxadviser.com/newsletters/2016/jan/congress-makes-changes-to-popular-tax-credits.html</a>

This does not apply to him, he has always had a SSN born here. So I should have no problems amending my return

Retroactive claims are no longer allowed for earned income credit (EIC), child tax credit (CTC) or American Opportunity Tax Credit (AOC) for any taxable year for which the taxpayer has a taxpayer identification number that has been issued after the due date for filing the return for such taxable year. That is, a taxpayer who files a return with an ITIN and later receives a SSN may not amend prior year return to claim EIC or amend a prior year return to claim CTC or AOC for a dependent who later received an ITIN or SSN.
reference:   http://www.thetaxadviser.com/newsletters/2016/jan/congress-makes-changes-to-popular-tax-credits.html