I never put in my real birthdate to any of these type sites. Just record whatever date I put in with my password and username for whatever account. Really don't remember having to put in my date for Bluesky, though I may have, was one of the earlier members by invitation, the whole registration process was a bit different. Bluesky has evolved quite a bit since then, still is evolving and improving their system. Their site was having a few temporary issues with the massive exodus from twitter x swamping their system, but they quickly got back on track.
Maybe you were dealing with those issues when you were trying to register. Also there's sometimes issues with how the date gets formatted, like single digits written double digit with a zero, or year in double digit or quad, and sometimes when you put in something like a slash between numbers causes an error due to the algorithms already accounting for the separations. You probably know all that, I know all that, but still have found myself correcting my error at times. Plus different sites have different data entry processes, you do one way, and it wants the other way.
Not sure why you might be having issues, but I would encourage you to keep trying. Pretty sure one needs to have their email validated, so if you don't get as far as the link sent, you will never be able to be registered and log in.
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