I haven't been able to find any information on this. How old does a kender have to be, to be considered as much of an "adult" as their kind ever gets?
From Dragon Magazine #101 (1985), All About the Kender by Roger E Moore, in a section describing the stats of playable kender:
Kender have the same lifespans and age categories as halflings, though they begin their adventures at age 20 + 3d4, regardless of class.
Thus we see that a kender will start adventuring (if they do) in their late twenties. (Earlier in the article we learn that "most kender are encountered during wanderlust, a peculiar phase that comes on a kender in his early 20s. "
This comports well with the Player's Guide to the Dragonlance Campaign (1993), which puts a bit of a more-definite point on the question of exactly when "adulthood" starts for a kender--before or after wanderlust?
Kender live to 100 years and beyond, always retaining their youthful flair for life. Adulthood begins around 20 years, and old age sets in at 70. As kender age, their faces retain a youthful appearance, save for a deepening network of lines and crow’s feet. Their hair grays gently, often starting at the temples. Kender consider this aged look attractive, and some accelerate it with mud packs to dry out their skin.
So if we take these to be canonical, it looks like around-twenty wanderlust is the beginning of adulthood, after 3-12 years of which a kender usually settles down. Or gets hooked and is officially a (playable) adventurer!
The Dragon article is predated, best I know, only by such information about kender as can be found in the DL-series of 1e modules and the first Dragonlance book.
- DL1, Dragons of Despair, only has the relevant line in Tas' backstory: "I've almost forgotten all the places I've been in five years."
- DL2 and DL3 have nothing relevant to kender ages, and the rest of the DL-series are published after the Dragon article quoted above.
- Dragons of Autumn Twilight, also published in 1984, doesn't mention Tas' age best as I recall; It certainly doesn't in the long-winded description of his first appearance on the road outside of Solace that I just re-read.
Wanderlust (Meetings, vol.2), of course, tells us more, but wasn't published until 1991.
From the Wikipedia article on Kender:
As they near adulthood, kender experience intense wanderlust and leave home. [...] The Annotated Chronicles cites the Dragonlance Adventures, which states, "Most Kender are encountered during wanderlust, a particular phase in a kender's life that occurs for most kender during their early 20s. Wanderlust may happen for many years ... and is responsible for spreading kender communities across the continent of Ansalon."
This matches what I remember from the Dragonlance source-books I used to own (first edition). If early twenties is "near adulthood", I would say 25 as a good, semi-arbitrary boundary.