I agree with Anastasia that the ideal time period for learning languages is during early youth and that children in general learn certain things more easily but I believe also that this is a a bit of an over generalization. Older learners can learn American Sign Language. It depends to a great extent on motivation and the techniques employed by the learner and their teacher. Older learners learn differently than very young children because they have a lifetime of learning experience under their belts. The strategies used to teach older learners should take advantage of their strengths as learners. While younger learners may "absorb" new languages through simple exposure older learners have pre-existing knowledge of how languages work. They have different cognitive skills that can be applied. They can compare and constrast. They have life experiences that can be brought to bear. In the proper learning environment, using techniques that take advantage of the older learner's existing skills and appropriate motivation they can learn ASL.
