Er...
Play the Aldmeri Dominion main quest.
I won't spoil anything, just play it...Especially the Reaper's March main quest.
The Mane is a unique breed of Khajiit. Khajiit tradition holds that only one Mane can be alive at one time and, more specifically, believe that there is actually only one Mane who is reborn again and again in different bodies. There has been no recorded incident of more than one Mane contending for power, although whether due to the truth in the Khajiit belief or whether the ruling Mane takes care of any potential rivals is unknown. Manes can only be born under a rare alignment of the moons Masser and Secunda when, according to legend, a third moon actually appears. In older days the Khajiit would shave off their manes in deference to the Mane, braiding them into locks which the Mane would incorporate into its own mane. As the population grew, however, this became impractical, although the Khajiit still remove their manes and the current Mane still wears the hair of its tribe and Warrior Guard which includes several hundred in number. The Mane is so weighted down by the hair that movement is difficult without aid and they often travel the countryside by means of a palanquin.
It doesn't really grow, or not all of anyway. Since The Mane, according to lore, is a separate breed/furstock, I guess we don't really know for sure. From the UESP Lore link the OP provided.The Mane is a unique breed of Khajiit. Khajiit tradition holds that only one Mane can be alive at one time and, more specifically, believe that there is actually only one Mane who is reborn again and again in different bodies. There has been no recorded incident of more than one Mane contending for power, although whether due to the truth in the Khajiit belief or whether the ruling Mane takes care of any potential rivals is unknown. Manes can only be born under a rare alignment of the moons Masser and Secunda when, according to legend, a third moon actually appears. In older days the Khajiit would shave off their manes in deference to the Mane, braiding them into locks which the Mane would incorporate into its own mane. As the population grew, however, this became impractical, although the Khajiit still remove their manes and the current Mane still wears the hair of its tribe and Warrior Guard which includes several hundred in number. The Mane is so weighted down by the hair that movement is difficult without aid and they often travel the countryside by means of a palanquin.