I don't know what kind of cactus
it is,, BUT from telling how spindly it is , it wasn't getting enough sunlight. It looks like it was "reaching for light" You could always cut away the longer spindly "arms" and repot them to start another one or two or three
or stick them in the same pot to make a fuller cactus
. I also suggest repotting it,, make sure there are drain holes.
As far as the White/grey area's it looks like a sign of aging,, YEP like humans they or a least ones like the one you have gets signs of age,, almost bark like surface( only smooth).
Hopefully someone else will come along and help you id this cactus
, and it's care.