Not that I'm really that serious a runner.
How many miles have they run? I don't know. For a while I considered calculating; working out my injuries and lazy periods, the recovery from my eye operation and hiding from bad weather and, of course, the cataclysmic hangovers. I couldn't be bothered. Why put a number on it when the answer's the same: they've seen a fair few. It's probably more than a thousand miles. They've run in Scotland, in England and in Ireland. They've run on both coasts of the United States: in California and Massachusetts. Sunrises, sunsets, and the glorious midday sun; howling gales, morning frosts and the odd hailstorm, their treads wasted smooth in all weather, at all times of day.
The heels wore out first and I repaired them with packing tape. The jury-rigging lasted me about a year.
I'd run the beaches and leave them on the landing outside the flat, coated in sand and/or mud. Some mornings they felt heavier than others.
In the time I owned them I changed jobs twice, ran four half marathons, gained more weight than I lost and didn't write anywhere near enough. I've been on three different continents and helped make three vintages of wine. The Red Sox have not won a World Series since, and the Celtics won one World Championship, their 17th. I attended several weddings but not my own. Many friends had kids, some more than one.
Can the lifespan of a pair of running shoes be a specific measurement of time? It's no more arbitrary than the calendar year, I suppose. A considerable chunk of life happened while these were my running shoes, and the breathless therapeutic rhythm of those daily exertions helped deal with the peaks and troughs of that life-chunk.
I've not thrown them away. They're in my closet, unworn since I retired them. Outside the front door of my flat sits a shiny new pair of Asics. I've run in them three times and they've given me some brutal blisters. My feet have healed now though, and I'm ready to give them another shot.
I don't know how long they'll last.