It’s perfectly feasible to be 4’4” at 18 for a variety of reasons, not all due to “dwarfism/achondroplasia” which I’m guessing is what the OP means by ‘proportion’. Humans come in a variety of shapes and sizes!
Dressing more formally may help you look older if that’s what you want.
Sadly people often equate shorter stature with younger age which obviously is often incorrect.
Not sure wearing extreme heals are particularly helpful, unless that’s what you want to wear of course.