I have all 5 children sleeping in the same room because my living room and dining room are also the sleep areas in the afternoon. The children all learn that they must be quiet for their friends and I soothe the babies to sleep, but occasionally one of the babies wakes up noisy and that's the end of naptime. I'm really lucky that they all sleep 2 hours before that happens most of the time.

Do you shush him and talk quietly to him to tell him to settle down and rub his back a bit and things like that? If you do a little of the soothing now he should learn that bedtime means relaxation.