Apparently Ukraine can't mobilize dudes under 27 (did we know about this?). New law they are drafting would lower it to 25. The article says specifically: "for combat duty", I dunno if this has any significance.
I'm aware that younger blokes fighting on the fronts since day one. Since 2014 basically.
https://www.reuters.com/world/europe/ukraine-draft-law-proposes-lowering-mobilisation-age-25-27-2023-12-25/

I tried to look up the Hungarian law about it, I found 2 that could regulate the age brackets, but could not find them in the laws. The rest of the laws about to homeland defence, military - judging by the titles - don't seem to be related to that particular topic. Perhaps I missed something.