Growing Pains and Stretch Marks Periods of relatively rapid growth (like teenage growth spurts and pregnancy) stress human tissues by stretching and even creating microtears. Magnifying the growth rate would magnify this effect. Growing up would be even more uncomfortable!
Growth Rate Imbalances Bilateral asymmetry, like my son's leg-length discrepancy, would be magnified by an accelerated growth rate. By shortening the time in which medical professionals can respond, this condition would be far more problematic. In instances of internal asymmetry, such as mismatched lungs or heart chambers, this would have fatal consequences.
Mismatches to Sexual Maturity If you posit that the time to sexual maturity is similarly shortened, people would have less life experience before being subject to reproductive stresses. Emotional development in this scenario would be radically different. If you assume that sexual maturity is unaffected by this accelerated growth, you end up with puberty AFTER physical growth; imagine 25-year-old teenagers. Either way, society likely becomes more chaotic.
Impaired Proprioception Even present-day children often find it hard to be aware of their body's capabilities and limitations as they grow. The big, clumsy teenager is a trope for a reason. Accelerating physical growth would increase this impairment, increasing childhood injury and death rates.
Child Labour For many cultures, children supply your family's workforce. Decreasing the time from conception to physical maturity will increase this cultural tendency, and increase its incidence in what we think of as more advanced cultures. This will come with attendant physicals risks to those children.
Nutrient Requirements Even if you posit that the rate of nutrient absorption failure in a population remains constant, accelerated growth will stress these cases further. Nutrient deficiencies will appear earlier, and be more severe. Increased caloric intake would also push this species towards a more carnivorous diet, along with all the attendant health risks and benefits.