Final answer:
Young athletes become more secure and aware of their identities in the late adolescence stage, typically between ages 15 to 18, when they form a more defined self-concept.
Step-by-step explanation:
Young athletes are more secure and aware of who they are in the late adolescence stage. Late adolescence typically occurs from ages 15 to 18 and is the period in which individuals experience significant cognitive, psychosocial, and physical development leading to a strengthened sense of personal identity. It is during late adolescence that individuals truly begin to answer questions such as "Who am I?" and "What do I want to do with my life?", and as a result, they are able to form a more defined self-concept. Meanwhile, the pre-adolescence stage is marked by the onset of puberty and the beginning of cognitive and psychosocial growth, but it's not until later that a more secure sense of identity is typically solidified.