I believe the "triple turn in" leves start at level 20.
Edit: to expand on that, you may see some leves before then that look like triple turn in, but aren't. For example, the Leatherworker Levequest
Skin off Their Backs ask for 3 Aldgoat Leathers, and it is a single turn in levequest. One tip off is that a triple turn in levequest that asks for an intermediate ingredient and not a finished product (i.e. squares of leather, ingots, etc) will ask for 5 of them, not 3.
Edited, May 6th 2014 3:10pm by svlyons