So if i understand you correctly the 17 year age limit is NOT based on 2019 but on 2020! and based on the entire year. ie. Becoming 17 on the last day of 2020 would define a child as No longer eligible.
**update **
As @Opus 17 has correctly stated, the child must be 17 at the END of 2020 to receive the stimulus.
Which explains my situation. See below.
**Under the eligibility rules by the IRS, the child must be under the age of 17 at the end of the year for the tax return on which the IRS bases the payment in order to receive the additional payment. Any dependent who is over age 17 and claimed on someone else’s tax return is not be eligible for the additional stimulus check.**
