@vinabomb So yours came after 15 years old. Girls, however, have theirs somewhere between 12 and 15, most noticeably getting bigger at 14. It's connected to a higher amount of unstable genetic information in the Y chromosome. We finish developing later. Takagi-san reflects that difference in maturity and resulting power dynamics pretty well.
My point is, due to sexual dimorphism, she still is supposed to have her growth spurt so the difference between 12 and 15 is supposed to be very noticeable because of it. Unless there is something I fail to notice in which case I kindly ask you to direct me towards that factor.