This is one of the biggest fallacies with learning to play the piano that I hear all the time: “You can’t teach an old dog new tricks!”. Well, this may be true for dogs but it just isn’t true for humans where piano is concerned.
Sure, there are certain facets about learning the piano that children will find easier - their brains are pure and malleable and take to some of the mechanical techniques easier. But adults are much quicker at grasping the theoretical concepts and have the added advantage of being able to GET. STUFF. DONE.
When I wanted to learn piano at six years old I begged and begged my mum to let me take lessons. I sat in on my older sisters lessons and became a pest - wanting to have a go myself. “Piano is your sister’s thing, Ruth” Mum would say, but I wouldn’t listen - Give. It. to. Me. Eventually, after I had painstakingly taught myself to play the beginning of Fur Elise as proof of my commitment, Mum allowed me to take lessons... I lasted one year. Now I wanted to learn violin and would simply die without it. My mum, bless her patience, took me to violin lessons. Fast-forward to when I realised that I really, really, REALLY sucked at violin and it was so hard that I ended up quitting after just two months and went back to piano! (Seriously, piano is much easier.)
But adults are much quicker at grasping the theoretical concepts and have the added advantage of being able to GET. STUFF. DONE.
The point here is at that age I did not have any staying power and most kids don’t. Nor discipline, nor fortitude, of any kind. Adults do. So you can feel good about that - you have decided, or are about to decide that you want to learn piano - you have all the human requirements needed to do that, provided you have some fingers (I’d argue you don’t even need ten). So you can stop using this excuse now.