Hi Timo,
I found a couple of studies regarding extreme sports:
1. Metal-on-metal resurfacing of the hip in patients under the age of 55 years with osteoarthritis
2. Five to eleven year follow-up of modern hip resurfacing: In patients under the age of 55 years with osteoarthritis
The studies followed 446 BHR or the precursor to the BHR resurfacings (384 patients) for patients under the age of 55 years (at the time of installation) where 55 % participated in impact sports or were involved with heavy occupational work. Impact sports is defined by the modified UCLA activity scale Level 10 "Regularly participates in impact sports as described above." Level 9 impact sports is described as "Sometimes participates in impact sports such as running, jogging, tennis, cricket, baseball, rugby, football (soccer), hockey, racquet sports, judo, karate and other martial arts, skiing, acrobatics, ballet dancing, back packing and mountaineering. Heavy occupational work."
There was only one failure from avn of the femoral head at a follow-up of 5 to 11.5 years.
I was 55 years, 25 days old when I receive my LBHR. I don't have osteoarthritis in any other joints or have problems with muscles, tendons or ligaments.
The results of these studies is good enough for me to participate in impact sports such as downhill skiing, hunting in the alpine (or mountaineering) and racketball. I don't run or jog outdoors since I didn't run or jog much before my hip resurfacing.
I don't know of any studies following patients regularly participating in impacts sports who received their BHR (s) at age 65 or greater but if your body is otherwise in great shape - go for it!.