That's a never-ending argument with some (including me
). Just to hopefully cut the usual noises short:
I view "loli" as a descriptive term, not an age bracket. Adult women can be "loli", people can dress "loli" and so on.
A fair number of folks view it as an age bracket. Even viewed as an age bracket there are disputes because the term derives from "lolita" which pegs the age bracket between pubescence and "legal" (varies by locale). A series like Moe-tan satirizes the "high school girl who looks like a 4th grader". Some fans include actual pre-pubescence ages (see the series Kodomo no Jikaan for reference).
As for myself, I call Taiga elfin or petite. I personally wouldn't necessarily call her loli unless she dressed the part. However, many fans call her archetype "loli-tsundere". She
might be also what is referred to as "
petanko" (small/flat breasted) BUT from what I've seen, she seems to have a figure appropriate for her size. The ratio between her and Ryuuji almost matches the ratio between my wife and I. Japanese women can be really small in comparison to European stock and still have a figure.
As a reference, my wife (japanese heritage) is 4'10" (147cm) and I'm 6'0" (183cm). Her weight is 95lbs (43kg) and that value has held true since she was in the 9th grade. Irritatingly but in the interest of full disclosure, my weight is about 210lb but I'm trying to drill down to 190lb (it was 225 last year).
I'm trying to find Taiga's and Ryuuji's height, no luck so far -- I doubt Ryuuji is much more than 5'8" (172cm) which would make Taiga about 4'7"(138cm) using ratios.
UPDATE: the Toradora! english wiki puts Taiga's height at 143.6 cm (4' 8.5") -- (the height of a couple of my wife's cousins). That means Ryuuji is probably 5'10" as well as Kitamura ... they probably got to know each other from being in the back of the lines together all the time.