"Decades" is the usual marketing answer. The useful answer is more specific.

The honest ranges

With regular wear — say, three or four days a week through autumn and winter — and reasonable care:

  • Full-grain cowhide: 15–30 years, often longer. The leather is rarely what ends the jacket's life.
  • Top-grain leather: 8–15 years. The applied surface finish is the limiting factor; it eventually cracks where the jacket flexes most.
  • Lambskin: 5–12 years. Softer and thinner, so it scuffs and thins faster, particularly at the cuffs and elbows.
  • Suede: 5–10 years, heavily dependent on exposure to rain and dirt.
  • Faux leather (PU): 2–5 years before the coating begins to crack and delaminate.

Occasional wear extends all of these considerably. So does owning more than one jacket.

What actually determines it

Leather grade

Full-grain keeps the hide's strongest fibre structure intact. A scuff on full-grain is a surface mark on a homogeneous material. A scuff on a coated top-grain is a break in a finish layer, and it will spread.

Construction

Look at three things:

  • Seams. Double-stitched stress seams — shoulders, armholes, side panels — last far longer than single-stitched ones.
  • Hardware. A YKK or Riri zip will typically outlast a decade of use; an unbranded zip often fails in two or three years.
  • Lining attachment. A lining stitched in can be replaced. A lining glued in cannot be removed cleanly.

Wear pattern

Daily wear in an urban winter is harder on leather than weekend wear. Commuting with a rucksack wears the shoulders and back faster than anything else you are likely to do.

Care

This is the variable most under your control. A conditioned jacket kept out of direct heat and stored on a wide hanger will outlast an identical neglected one by years.

What fails first

Almost never the leather.

The zip is the most common failure. It is also the cheapest fix — a leather specialist can replace a main zip for a fraction of the jacket's value.

The lining is second. Viscose linings wear through at the underarm and the pocket bags over years of use. Relining is routine work.

Stitching at high-stress points can give way. Re-stitching is straightforward.

The leather itself typically fails only through neglect — cracking from being allowed to dry out, or rot from being stored damp.

This is the practical argument for buying good leather: the parts that wear out are replaceable, and the part that is not replaceable is the part that does not wear out.

Making it last

  1. Condition once or twice a year. The single highest-return maintenance task.
  2. Store on a wide hanger, out of a plastic bag.
  3. Dry it naturally whenever it gets wet, away from any heat source.
  4. Rotate it if you can. Leather benefits from a day to recover between wears.
  5. Repair early. A small seam failure caught quickly is a ten-minute job; left alone, it becomes a panel replacement.

What "patina" actually means

Patina is the uneven darkening and softening that develops where a jacket is handled and flexed most — across the shoulders, at the elbows, along the zip line, around the pockets.

It only happens on aniline and semi-aniline finished leathers, where the dye penetrates rather than sitting on top. A heavily pigmented leather will stay looking new for longer and then look worn rather than aged.

If you want a jacket that improves rather than merely survives, that is the finish to look for.