"I know I should take better care of myself but I am still young so I don't have to worry about my diet, sleeping habits, exercise, etc"
When we are young, we tend to live in denial of our mortality and as a result, we erroneously think that we can abuse our body with unhealthy diets, late nights, work stress and inadequate rest. Not only do we wear our bodies out earlier with these bad practices, we also risk them becoming habits of which will be very difficult to change even when we want to when older.
1) Never use your age as a reason as there can be no excuse to wreck your body. Your body and mind deserves to be respected.
2) The younger you are, the easier it is to form good habits, so start having healthy routines and habits as early as possible.
3) You can just do it. You will realise that living healthily (ie, adequate exercise, good sleep schedules, adequate rest and moderation in food and alcohol) is not hard to achieve at all and will help you feel both mentally positive and physically attractive.