Age matters. How much it matters depends on your lifetime goals. Do you want to simply have fun and make music for yourself or family? Perhaps you have greater aspirations. In the latter, age matters very much. The window of greatest opportunity begins to open at about the age of two, is fully open between the ages of seven and fifteen and is nearly closed by age twenty-five. Is there a best age to begin?
Here's my personal experience.
I come from a musical family. One distant relative was a Austrian composer and organist in the early eighteenth century, (no one well known). My grandmother was church organist and her mother and father were both violinists and pianists. My great grandmother was also an organist and a pianist. My father, grandmother and great-grandmother had perfect pitch. I inherited this trait. Sadly, all my grandparents died before I was two.
Once when I was three, I watched Tom play Liszt's Hungarian Rhapsody #2 while Jerry dodged the hammers. I didn't know what it was, but I loved it.
Growing up in 1980's America, I felt culturally like a duck out of water. I couldn't identify with the popular music. I was a very sick child, barely able to breathe from asthma. I found solace in my father's stereo, always playing the great classical works. We had a piano, but my parents didn't play, so it was more a piece of furniture than an instument. I never touched it.
I learned to read music when I was 7 (I played the trumpet and the recorder for a couple years, just kid's stuff). Only at 13 did I show an interest in playing the piano. One day, I cracked open the lid of the old Wurlitzer, which hadn't been tuned in twenty-five years. The sound was awful, I could get a tri-tone by playing one key! After much begging, my parents bought a new piano, the clattering Wurlitzer was replaced with a very nice upright. I was in heaven.
On the piano, I was somewhat of a prodigy or at least precocious. Before I started lessons, I had learned the first movement of Moonlight Sonata and Fur Elise and was attempting Chopin's "Raindrop Prelude". Having learned to read music only in the most basic way, I could barely make sense of the scores. My will was strong. After one year of lessons I played Maple Leaf Rag, Mozart's easy C major sonata and a complete Beethoven Sonata well.
Now, 13 years later, (in good health, thank God!) I've learned 26 Beethoven Sonatas, most of Mozart's Sonatas and about a half of what Chopin wrote, lots of Bach too, only recently adding piano concertos to my repertoire. At the age of 27, I'm improving very rapidly, both technically and especially artistically. I refuse to call myself a virtuoso, it just seems so egotistical, not to mention beside the point.
Had I started at a younger age, I would most definitely be a professional concert artist by now. God only knows where I'd be. It begs the question, "should parents force a talented child to take lessons at five, when musical aptitude is obvious but the will to practice is none?" NEVER!!! Forcing could instill a lifelong disdain of the instrument. That would be a far greater handicap than the one of starting later. If any parents out there have a talented young child, concentrate on letting him be expressive without making a contest of it. The artist who starts late should have no regrets. Do not equate artistry with virtuosity. Artistry is the goal, or (unfortunately) in many cases, it should be. In my opinion, virtuosity is simply a side effect of artistry combined with hard work and should not be a goal in isolation.
A pianist's full potential can only sometimes be realized starting at a late age. I don't mean to say "don't start to play the piano if you're not a little kid". Never say, "never." Anything is possible. Just be realistic, don't assign limits to your potential and most of all have fun!
The piano can give joy to anyone who enjoys it. Is that not the point? How easily we forget.
Per Sapientiam Felicitas!