37 years old am I too young for a total knee replacement?

Not necessarily. While 37 is very young there are some circumstances where a total knee may be indicated. Before considering this however, there are a number of other options available that you should discuss with an orthopedic surgeon. These may include rehabilitation, bracing, medications or injection therapies, arthroscopic procedures, cartilage repair, osteotomies, and partial replacements.
Yes. Total knee replacement has a limited life span and we try and delay until absolutely necessary. That being said, there are patients with rheumatoid and other arthritides that might be a candidate. Weight and activity level has alot to do with longevity of total knee.