I'm 42 and was not a strong quant student when I was in college over 20 years ago. I would absolutely agree with the other posts that depending upon your baseline knowledge, you may find yourself needing to re-learn the basics, before you can start tackling the tougher problems that will come your way. This means a bit longer of a runway before you jump into the regular GMAT study plan. A GMAC GMAT practice exam will help you learn how long of a runway.
I just finished working through the Kaplan Math Workbook Edition 6 to give me the foundation and now will be moving into the OG books. The beat the gmat forums and articles will tell you everything you need to know to prep yourself. The advice about analyzing practice problems to learn be able to master the problem is really key. Finding this website has been hugely helpful, from the ability to post a problem that you don't know how to solve (and get an answer from someone on the other side of the world in as fast as an hour) to the success stories, study tips and practice problems.
From my vantage point, scoring well on the GMAT has been and will be a massive commitment for me. In order to keep myself motivated, I visited the top three schools that I plan to apply to for an EMBA program and sat in on classes. Being in that academic environment observing world-class professors engaging a class full of bright, accomplished professionals was incredibly energizing.
I truly believe that one advantage that those of us over the age of 40 have is experience with dealing with difficult and challenging obstacles in life (likely far more impactful than the GMAT) and that deeper perspective will help you keep an even keel should your runway be a bit longer than those just a few years out of college.
Go for it! You'll learn a lot about yourself in the process.
