There are essentially 2 means of looking younger: by reducing the pace of aging and using cosmetics/surgery.
The former requires you to look after yourself. Out of the 6 factors, chronic long term stress is one of those factors that speeds up aging (do note, this is not the same as temporary stress e.g. in exercise workouts - that's actually healthy). So yeah, according to the experts and researchers on aging, being less stress will make you look younger. Happiness is a bit vague, but having good social relationships with people tend to help with aging, and social relationships tend to be associated with happiness (we are social animals after all).