My understanding is that tunics are the "shirt" equivalent for little boys. They are the stage between a dress and a tucked or buttoned-in shirt. Marta has done a more thorough evaluation of CDVs for tunics and I think she stated in another thread that they are very common until about the age of 10. There seems to be some variation due to style preference of how long boys would wear a tunic, versus a shirt, similar to the age boys would move to long trousers instead of short ones. The transition tends to be along class lines, an upper class boy would be more likely to remain in tunics and short pants longer (to keep him looking childish) while a lower class boy would probably adopt long trousers and shirts sooner for practicality reasons. Personal preference plays a part too (including that of Mom

). Hope that helps your research!
Thanks Lissa. That about covers what I've found in my (prrimarily) pictorial research. There are tons of fashion prints that show boys in a wide variety of tunic styles and a fairly big age range. Generally tunics appear when a boy is reliably out of diapers, and will continue as long as mother wishes (up to about 8 or 9) or as long as they are practical for his family's economic level.