The dorsal spines are often used in studies on the age and growth of tuna. However, there are vascular tissues in the central area of the spines that make difficult the estimation of the number of growth increments. Some growth increments are missed as the organism and as the central vascular tissue grows. Therefore the age estimations can be biased (i.e. underestimation). In this work we propose methods to minimize the biases in the age estimation of tunas, and we show an application for the skipjack tuna (Katsuwonus pelamis), which is a very important fishery resource. The growth estimations using the best corrective method (L8 =97,9 cm; k = 0,14 por ano; to = -0,071 anos; r2 = 0,71) were very different from that gathered by not trying to minimize the biases (L8 = 80,6 cm; k = 0,25 por ano; to = -1,94 anos; r2 = 0,27). If the results from the corrective method are more reliable than the others, the scientific opinion on the skipjack life history should change. The skipjack would has a longer life history, reaches larger sizes, and grows slower than one could deduce relying on the traditional estimation procedure. The multiple regressions are good tools to correct aging estimates, when it is difficult to identity growth increments in a part of the aposition structure (e.g. spine) being analyzed.