Implicit skill learning underlies not only motor, but also cognitive and social skills. Nevertheless, the ontogenetic changes in humansʼ implicit learning abilities have not yet been comprehensively characterized. We investigated such learning across the life span, between 4-85 years of age with an implicit probabilistic sequence learning task, and we found that the difference in implicitly learning strongly vs. weakly predictable events exhibited a characteristic and rapid decrement around age of 12. These lifelong learning efficiency measurements support an extension of the traditional 2-stage lifespan skill acquisition model: in addition to a decline above the age 60 reported in previous studies, sensitivity to raw probabilities and, therefore, acquiring fundamentally new skills is significantly more effective until early adolescence than later in life. These results suggest that due to developmental changes in early adolescence, implicit skill learning processes undergo a marked shift in weighting raw probabilities vs. more complex interpretations of events, which, with appropriate timing, prove to be an optimal strategy for human skill learning.