<prompt> Birth length doubles by what age?1 year2 years3 years4 years  <response>: Ans. d 4 yearsRef :O.P Ghai 8th ed 15TimeLengthAt birth50cms3 months60cms9 months75 cms2 years90 cms4 years100 cmsIndian children gain 5 cms height every year until 10 years of age. 