Not a native and not entirely sure whether it works here but generally you can use a’ fàs, lit. growing, for becoming, getting some way, for example (from Colin Mark’s dictionary): bha a lèirsinn a’ fàs sgleòthach his vision was becoming misty / misted, tha e a’ fàs sean he is getting old, … tha iad a’ fàs nas eòlaiche air teicneolas … they are becoming more familiar with technology, etc.
So I believe you could say: tha mi a’ fàs maol for I am getting bald.
maol also is a verb meaning Make blunt, bald or bare. 2 Become so. 3(DU) Cut one's hair. acc. to Dwelly and 1 blunt! 2 make bald! 3 bare! acc. to AFB. But Colin B.D. Mark doesn’t list it and I cannot find any good examples of usage related to hair on Google (most results are either lyrics of a song not related to hair, or some automatically translated spam websites).