I recommend learning a skill/hobby that becomes a positive part of your on-going lifestyle. Personally I am learning more skills that involve my health, safety, and communication skills. For my health I am learning more about nutrition, internal medical theory/practices from Asia, cooking, yoga, and martial arts not only for self defense but for philosophy and oneness. For safety I am learning survival skills involving water purification, fire, first aid, land navigation, marksmanship, in addition to martial arts. Lastly, for communication I am focusing on toastmasters for public speaking, ham radio, and sign language. I feel many of these life skills useful will remain relevant regardless of my age and would help others if shared too. Your mileage may vary.