Horn Buds Horn tissue starts growing from birth, but bone doesn't start to develop until 2-3 months

Loose Skin As babies, tiefling have prominent scruff until right (around) 3 years of age. Depending on the variant of tiefling, some parts of the skin might still remain loose to help the body remain flexible while running and jumping. (Other spines, spikes, and ridges will start to show as the body fills into its loose skin.)

Tail Variety The development and grwoth of a tiefling's tail depends vastly on the individual it belongs to! Spikes, spines, and other bone growth might grow at the same rate as their horns, but some don't develop until puberty (and some don't grow anything more than the initial tail bone at birth).