Will the ECR status on my Indian passport be automatically invalid after I turn 50 years old, or do I need to apply for a new passport after I get 50 to remove my ECR tag?
ECR status of passport is indicated by a physical stamp on the passport. Absence of stamp makes your passport Non-ECR.
Though I cannot find any canonical reference, the insistence on ECR stamp in the MEA website makes it look like as long as your passport has this stamp, you will be considered an ECR person.
To remove the stamp you will have to apply for re-issue of a passport. In the reasons for reissue on the passport website, they even have a separate column for it: "Deletion of ECR"
In your case you would attach a birth certificate and your re-issued passport will not have ECR endorsment.
Please note that ECR passports are equivalent to normal passports if you are visiting abroad on a non-employment visa (Source is the quoted MEA website).