Rule # 1 Get a passport.
Rule # 2 Get a passport
Rule # 3 If you have any questions reread rule # 1 and 2
In this day and age anyone (any age) who gets on a plane or cruise ship should be travelling with a passport. Sure you can have raised seal notorized copies of letters from your mother and official Boy Scout ID cards as well as your Video Rangers and
even Sky King official club membership cards (boy did I just age myself). But,
NOTHING BEATS A PASSPORT. It is cheap, easy to obtain and it is literally the best form of ID in the World. Why chance a couple of ticket agents or embarkation clerks who have had a bad hair day over "questionable" ID? Why stand and argue while your plane takes off for paradise? And believe me, you do not want to get into an arguement with an immagration officer (in any country), you will not win.
Summary GET A PASSPORT.