What to do for the pacing, lurking, from living room to bathroom, contently?

Pacing may indicate that the person wants to use the toilet but if he has always been active and walked regularly, he may be feeling frustrated and want some fresh air. Perhaps you could take him out. Some people just want to pace though and much as it may drive you nuts it's what they want to do and as long as they are safe let them. You may also want to use something to distract them like helping you make something or looking through an old photo album. If as you say that stops the pacing then it may need some seriosu thought as to what he likes to do that would distract him ...perhaps a jigsaw?