The question seems a little confused to me. At face value; if you have beaten Maat before on another job, your path to 75 on any subsequent job is clear of any level restrictions.*
As for fighting Maat on WHM, you don't need to defeat him by means of dealing damage, though that option is open to you should you choose it. The more popular (and somewhat easier) strategy is to simply let him hurt you and cure yourself. After you've cured yourself for a set amount (I really can't recall the figure, it's been 4+ years now, but I'll take a stab at 3000 HP) he gives up.
*NB: Bear in mind this only applies to the jobs that actually fight Maat for the level cap. ToAU/WoTG jobs fight someone else entirely.