change attribute with /mage attribute health_max 23 didn't work

Builtin attributes are not writeable. They are just there to advertise values like health, mana, etc to spells.

I would not recommend changing your max health directly anyway, you should use attribute modifiers for that.

oh... then sorry for bad report :(

That's ok!

It might be a nice feature for some sets of attributes ... but for max health I do think it's a bad idea to modify the vanilla attribute directly, versus putting a modifier on it.