ENIAC (first general-purpose computer)?
I can stand, but I don't have legs
It was a large computer consisted of multiple boxes which literally stood on the floor (ENIAC occupied a large hall) without having any legs.
I can eat without a mouth,
Card reader "ate" the punch cards to read information.
I can smell without a nose
Tube burnouts etc. was common upon operation, so I believe it actually smelt of something.
I can see without eyes
Again, card reader "saw" the information punched on the cards.
But I can't do what I'm not allowed to
Of course, like every computer, ENIAC performed only the commands which have been ordered.
ENIAC is now disassembled, so it's no more of it now.
Obviously, "ENIAC" is 5 letters long.
Card punch for outputting information allowed it to "speak".