Tolkien kinda sorta sez Elves are immature until 50, at which time I presume they start their adolescence. I would 'guess' adolescence would last until 70-75. They go through long courtships and marry for life. They are immortal, but can be slain. They also can die of grief and some diseases.
D&D sez Elves live to be approx. 700 years old. When you meet Xan he is already a L2 or 3 magic user and he has gone thru the "moonblade" rite of passage.
So, using these two 'sources', I would guesstimate Xan is somewhere between 100-200 years old, probably unmarried, and is considered mature and level headed enough to be assigned quests by his leaders.
I have no idea about the details of reproduction, but since Elves and Humans are close enough to mate, I assume the process is....ahem....similar.
