I read a comment by Tim Janof about starting when you are older - he says: "I think it's a little more difficult when you are older since you (we) have to contend with our own egos and "wisdom," which tends to cloud the learning process. But if you are patient, you can do it!"
I respectfully disagree with Mr. Janof…Now, I only have four lessons under my belt but I'm surprised at how quickly I have been picking it up. I don't think that it's in spite of my age, but because if it. It's that "wisdom" that Mr. Janof mentions that I think helps, not hinders. I do have those piano lessons to compare (between learning an instrument when young and old) and I noticed myself grasping concepts much quicker than I did or could have at a young age. For instance, when young, of course, I wanted to immediately learn to play songs. After the first cello lesson, I recognized how important learning to play scales and "tuning in" my fingers was. I don't think I would have had that insight as a youngster. I also immediately saw the importance of posture and playing position and how to hold the bow. I actually think my motor skills are a little more finely tuned than they were when young. And finally I instantly understood the importance of mentally connecting the notes I see written on the page with a sound and position played on the cello - something that would take much much longer to grasp when young.
OK, like I said, only four lessons, but my family actually likes to listen to me play already so that must be saying something (although my son says he's already bored with my limited repertoire of songs). I even played a duet of "Alouette" with my 11-year old son (who has started lessons recently) on the piano - which was pretty cool, and I think I have inspired him to work harder on his piano lessons and now my 6-year old daughter wants to learn to play the violin (which is great).
On the other hand, I'm sure there are many advantages of starting young. There are the years spent developing that muscle memory when those muscles and brain synapses are still developing. And then there's just the time practicing. I'm sure I will never play the cello in an orchestra, or even a string quartet for that matter (although that may be a goal to shoot for). Why, because it's the TIME that it takes to become a master. As Malcolm Gladwell says in his book "Outliers" (I recommend reading it) it takes on average 10,000 hours practice to become really good at anything. I just don't have that much free time to practice left! So I will be content sitting on my balcony and playing "Amazing Grace" for me, because it's satisfying, and relaxing, and will probably help prevent Alzheimer's. But it's certainly not too late to start - probably just too late to become really good!