You will find that shops in the Red Sea will insist on a refresher of some kind after as little as 6 months out of the water. One of the shops I freelance for here in Sharm insists on a check dive after 6 months away from diving - it costs a few euros more and the instructors basically review a few of the more important skills and then go for an easy dive to determine the divers' comfort levels before they hit the more advanced sites. I think a scuba review is required after 18 months.
After 4 years you may wish to consider a scuba review or find a buddy and go and do a few easy dives before head off to the red sea (if that's possible in your location) .
Practically speaking, it won't make much difference to your holiday. Enjoy your time here!
Cheers
C.