I'm 29, pre-nursing, and am still asking myself the same question. I'm going to do my nursing degree, and if I kick myself and want to pursue an MD. title down the road, I will.
Only you can make that choice. Check out a shadowing program at a local hospital, and see if you can spend a couple of hours on the floor with a nurse. That will give you a good idea if you are headed down the right path.