Was 23 Worked full time and attended school part time and did not receive EICTurbo Tax says due to age?

Does it think you were a dependent?   You needed to be a full time student to be a dependent under 24.  2020 and 2021 had special rules, there was no age limit and you didn't need a child to get the EIC.  But are you trying to do 2021 in the online version?

 It's too late to start a 2021 online return or use the mobile app, either on Turbo Tax or the IRS. And too late to efile 2021.  If you need to start 2021 you can buy the Desktop download here,

TurboTax 2021 Prior Year Tax Prep - File Past Years' Taxes

You will need a full Windows or Mac to install it on.

To get the EIC for 2021 without a qualifying child, if you were at least half-time in school you had to be at least 24 years old.

There was no maximum age, but there was a minimum age. You had to be at least 19. But if you were a student at least half-time, you had to be at least 24.