There’s a form (isn’t there always?), but it’s not terribly burdensome. Here’s the link for MCPS information on age requirements for enrollment.
https://www.montgomeryschoolsmd.org/info/enroll/requirements/
Apparently, there was a DCUM thread a while back discussing a rumor that MCPS may be changing its policy about redshirting. As far as I know, there hasn’t been any confirmation and this is only an empty rumor. (Frankly, I suspect the schools would prefer that students who need a little extra time to mature get it, rather than coming to K before they’re ready, but that’s just my perspective.) However, you might want to confirm the policy with the school system directly, before you commit yourself by moving.
https://www.dcurbanmom.com/jforum/posts/list/1298656.page
Redshirting tends to be a hot button topic on DCUM, and you may receive some rabid responses. In real life, I don’t think people most people will know, much less care, how old other kids are when starting K.