I get the same "OAS over the Limit Warning" every year when entering OAS payments.
The T4(OAS) Warning is not something Turbotax can calculate accurately since the OAS payout amount will depend on what age a tax payer decided to take OAS which TurboTax will not know. Delaying the start date of OAS payments provides a higher payout above the normal amount. All TurboTax can do is give a warning if it is over the max for taking it at the normal retirement age.
