This is a remix of (https://www.thingiverse.com/thing:2169921) all I did was add the english and japanese pokemon logos. It fits a new 3dsxl in a case. It WILL fit a new 3ds xl outside of a case but its a little loose and could be bad on the charge port. But you really should have a case on your 3ds X-D I have no idea if an old 3ds xl fits or not but I assume it does.
Since the walls on this a fairly thin you might want to use 20%+ infill. I printed mine with supports and it came out perfect.