Continuously failed in big tech interviews...I am 54.

Currently I am in public sector (state government) and have tried big tech companies for last 12 months, I went to final interview rounds with 3 big tech companies so far and all failed.

What is my improvement item?

Is my public sector resume not attractive to big techs? Or practically am I too old to try a big tech where hiring managers seem 15 years younger than me?

Thanks for your input in advance.

(Added later) I have 19 years experience in supply chain mgmt in both private and public sector..currently I am at state government....I was mostly applying to sr mgr positions in big techs....thanks for all advice.