I'm 38, I have been told I should have a hip replacement, is this too young or should I wait?

No. Thirty eight years old is young, but not too young, to consider a hip replacement. If you have exhausted all other options, includinig intra-articular steroid injection & anti-inflammatory medication, and you are at your ideal body weight, you would be a reasonable candidate for either hip replacement or the more controversial hip resurfacing (not recommended in women of child bearing age).