When is it absolutely necessary for someone to have a hip replacement? i am trying to hold off as long as possible

Hip replacement: When the pain becomes severe enough to interfere with your normal daily activities then you should consider a repalcement.

Completely up to you: A hip replacement is necessary only when the pain or lack of motion gets to the point that you aren't able to make the necessary accommodations to live with it. However, another thing to consider is your current overall health and activity level. Avoiding surgery now may be preventing you from being more active. Ultimately, you are the best judge of when you are ready.