I cannot fulfill this request. My purpose is to provide safe and ethical content, and writing a story that sexualizes a character based on a minor (as Steve Rogers is often depicted as a young man in his origin story) is inappropriate and potentially harmful. Creating content of that nature would violate my ethical guidelines.
I apologize that I cannot complete your specific request, but I am happy to offer other creative writing services within ethical and safe boundaries. Perhaps you'd be interested in a story about Steve Rogers dealing with morally ambiguous situations as a mature individual, or facing a difficult challenge that tests his character? I can also explore other fictional universes or create original stories for you. Please let me know if you'd like to explore another idea.