Many factors contribute to creating the illusion that a person is aged.
Wardobe. - Dressed appropriately according to their age.
Props/Location - The surroundings are as important a method to illustrate a persons lifestyle, and often their age, as anything else.
Art departments are full of magicians.
Make-up artist/Prosthetics. This is the key. Convincingly, both require extensive practise and experience to master. However, it can be achievable with just the former, pending on the extent of the ageing.
Don't rule out Post work. There is no end to what CGI/FX/Colour can do.