i know a guy named Kai and he's in his 30s. I think it ages well.
According the 50,001 Best Baby Names by Diane Stafford book I have:
Kai
(hawaiian, african) attractive
Kay, Keh
According to The Baby Name Wizard by Laura Wattenberg book I have:
Kai
Popularity: # 265
Style: androgynous, brisk & breezy, little darlings, scandinavian
~ A popular name in Northern Europe, also used in Hawaii. You can sense both styles in Kai, giving it a particularly refreshing feel: a ski trip and beach vacation all in one.
Any middle name ideas?