biggest problem you will have, getting the big tiles flat and even with each other.
Walls are by nature, not really flat, shower floor by design is sloped to the drain.
Sure you can use 12"x12" tiles, smaller 4"x4" or 6"x6" are more forgiving and easier to set.
For the floor, the small 1"x1" or 2"x2" that come in 12" sheets are really easy to set.
Just the bigger the tile, the more complications you run into.
Same with a kitchen floor, 12" tile is fine, start going to a 18" or 24" tile. floor better be real flat and will take patience to lay them.
Again, using a 1/8" grout line means you better be good, a larger grout line will hide many tile imperfections while being laid ... 1/8" you have no room for error, every bump will show next to the joining tile.
So answer is yes, you can do this .... just be aware of the issues you will face while laying it.
Be patient, take your time .... will come out great.
12" or even larger on walls are no problem. We have to assume the substrate is flat within standards though. You have to fix most walls these days.
Use tiles that are less than 4" on shower floors unless you build the floor to incorporate a linear drain which has only one plane. Normal traditional shower floors are dished, so no large tiles can be used.
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