Complex sentence: At the age of 13, he went to his 3rd venture-Pigeon Busters to catch pigeons and selling them to hunters for dog training which he continued throughout high school before giving it to his younger brother, when he left for college.
Split into simpler sentences: At the age of 13, he went to his 3rd venture-Pigeon Busters to catch pigeons and selling them to hunters for dog training. Brandon kept this business throughout high school and gave it to his younger brother when he left for college.