I've been mulling over how to represent aging in Dresdenverse for a little while, and it is particularly relevant to the Gold Coast, so I'll provide my current thoughts:
Aging is a set of consequences; each either reduces your refresh by 1 or renders a physical Stunt unusable (you still know the stunt though, and can teach it - allowing the possibility of the Aging Master who can train you in things they can no longer do).
Middle Age is a Moderate consequence. This reflects the unpleasant reality that bumps and scrapes you can shrug off as a teenager have an annoying habit of hanging around for weeks or months. On the upside, the character gains an additional 5 skill points, that can be placed in mental or social skills. The character likely has a 'spare tyre' or other indication of flabbiness caused by the stresses of the last decade or so.
Middle Age does not heal, but can be bought off; simply pay for the granted skills points. Any character can buy off Middle Age, including those who are Old or Dying - this reflects the elderly who are still in hale health.
Old is a Severe consequence, and provides 10 skill points. Mundanes cannot buy off Old; the character requires at least Wizard's Constitution to do so. It is otherwise the same as Middle Aged. Characters can possess both Old and Middle Aged but need not do so.
Dying is Extreme, and provides 15 skill points. The character must have spent Refresh on regeneration to be able to buy off Dying. Note that as an Extreme condition Dying also changes one of your Aspects. Otherwise the same as Middle Aged and Dying.