Re: 718 Boxster tire life?
I have a 981S and will assume the 718 should be in the same ballpark. I got over 15K from my last set or rears (Goodyears from prior owner). On my 987S I'd get 15-20K on the rears.
Add another recommendation for Michelin Pilot Sport 4S. Great tire, much nicer than the Goodyear I had before this. It seems to be the best all around summer tire from what I read (works fine in rain for me as well).
Since you are seeing wear issues I'd have it aligned (front and rear) and the suspension checked for issues. Get that done by someone who knows these cars, ideally.
2015 CS, Carmine Red, PDK, PASM, SC, 20" Carrera S Wheels in Platinum Satin, Premium Package Plus (Entry&Drive, etc), Power Steering+, PDLS, 18 way Sport Seats, ACC, Rear Wiper!
Previously 2008 CS, Cobalt Blue, PASM, Stone Grey, Sport Seats, ACC, Bi-Xenon, Sport Steering Wheel, Park Assist, Sport Exhaust Tip, Fire Extinguisher, Rear wiper