Letters to the Editor. "Putin et al.  just published an excellent article showing how machine learning methods (specifically deep neural networks, DNNs) can be used to quantify the aging process using a set of 41 standard clinical biomarkers, most of which are not specifically recognized as biomarkers of aging. DNNs provide a method to obtain a predictive algorithm from raw data (the biomarkers in this case) with minimal to no a priori assumptions (see Mamoshina et al. 2016  for details) [...]."