They already have the data and much more of it. This has nothing to do with “Big Corp” wanting to know how old their users are.
It's not about the age, but whole identity. You know you are serving ads to a real person and not a bot and so on and you can correlate person across different services with 100% accuracy. Currently you can still reasonably easy fake a persona.
Meta is the largest sponsors of these bills... https://old.reddit.com/r/linux/comments/1rshc1f/i_traced_2_b...