I'm not sure but I'm pretty sure it's either 4 or 2 years, because the keyword is "gently", which means that he did it soft if he were to comb out the hair soft many hairs wouldn't fall out, but if you had old hair up to 2 - 4 years then I'm pretty sure the hair would fall off if anyone is confused on which one to choose I recommend 4 years because it's longer but if it was 4 years more hair would fall off so it actually might be 2 years just read this through and see which one gravitates more to you.
C. 2 Years