Hi Patches, welcome to the site. I see you're 24 - we've had several other people who have had the bad fortune to lose cartilage at a young age.
Dannywayoflife was 28 when diagnosed, had his done at 29 (pretty sure), he can fill you in on his thoughts and feelings on the matter. Several others have also had theirs done at a young age, one I remember (whose Mom was on here) was 12.
As to the longevity, we are the first generation of large scale users for this type of device, so all I can point you to are the national registries, the most reliable of which (to me) is probably the Australian registry.
Their record of success, as measured by not needing to be revised to a total hip replacement (THR), is on the order of 96% at the ten year mark. Ten years are as far as they have measured, so at that point, with all doctors good and bad, with devices, most of which have been good, but a couple that had flaws and were recalled, that is the overall rate of non-revision.
No one can predict the future, but given the statistical results so far, it is encouraging to see strong performance from the HRs that folks are now using. There are anecdotal stories from people who were really ahead of the game and have had a an HR for 20+ years and are going strong, but they are not something you can bank on when you are looking at statistical results. Nice stories, though.
I've treated it as something that gives me back my life when I can use it, and if the time comes when I need to revise to another HR or a THR, I'll be thankful for the good years I've had.