The notion of a critical period, the period after which learning a language natively becomes impossible (Lenneberg, 1967), has been replaced by the notion of a sensitive period, which is much more fluid, individually variable, context sensitive, and based on what languages X, Y and Z are (e.g., Kuhl, 2005). The critical period was observed to be around 6-8 years old, but a sensitive period can account for the fact that grown adults can become native speakers, especially if languages X, Y and Z have similar, overlapping phonologies. See also Finn et al., 2013 for a neural account.
So theoretically, if you have learned a language or skill that is similar structurally on a neural level, you could pick it up.