How does a young person rid himself of pessimism and a negative outlook on his future and life?

These are whisperings that Satan casts into your heart to come between you and your well-being. Therefore, you must repel them and cast them out. What will help you with this is to recall the great blessings of Allah upon you, to have good thoughts about Allah, to submit to His حكم (judgment/ruling), and to be content with His قضاء (decree) and قدر (destiny), knowing that Allah is more merciful to you than a mother is to her child. So, if you fully entrust your affair to Allah, then take the means that bring success, and thereafter, let your heart be attached to Allah, the Causer of causes. Strive in supplication for Allah to remove these thoughts from you and to fill your heart with tawhid (monotheism) and trust in Him.