Wet dreams

hi guys and gals
recently my husband, who is 22 years old, has began having wet dreams. this started about three months ago and on and off he'll have a wet dream. we have sex at LEAST every other day, so i am confused as to why this is happening to him, i mean, isnt he a little old to be getting wet dreams, specially since we have such a great sex life. i wonder if this is anything for us to worry about. any insight would be great!!!!