"Oh, I am already 46, why should I start to learn an instrument? This train I missed a long time ago...."
No! The human brain is able to learn for your entire lifetime - yes, it is indeed a necessarity in the human being: constant learning. We learn every day even until we are very old. Why do we have the opinion, that an adult can't learn an instrument anymore?
Of course as a late beginner you can not expect, that your skills are ever comparable to a child beginner. An adult beginner can never catch up this early mover advantage .
But a nice sounding musicplay is possible later too. It is never to late to start something new and if we are looking at it from the other side, we can see the 20,30,40, X years we can play music ahead of us. This can easily be many decades (!!) for an young or a midage adult!
One of the biggest advantages of adult beginner is sure the high motivation. Adults have a better mental comprehension for theory and you can easily practice for 1 - 2 hours a day in motivated phases and can work really properly on a specific training. Of course the young beginners get this theoretical knowledge in their teenager years too and they sure have a better physical training until then. Even that good, that an adult beginner can never catch up.
But hey, aren't we playing music, because we wanted to listen and play these wonderful creations ourselves? Music is deep inside everyone of us and it is such a good feeling, being able to play something that beautiful ourselves. We don't need to be perfect and don't need to have unreachable goals. Having fun on the selfmade music is the main goal. That is the beauty of music and this is worth striving for us adult learners too. And it can be reached!!! ;)
When I started to play piano as a late beginner, I learned autodidactic for the first months. It was OK for a certain time. To read notes is just theory and application - almost like learning a language. More difficult was the training of specific handmovementes and position of the chair or the arms, hands and fingers. After some months there were a lot of questions about how to manage everything with rhythm, with both hands playing different rhythms, chords, dynamics and so on. At this point I hired a teacher. Now I go to pianolessons every 2-3 weeks and I make good progress right now. The exercises for rhythm, dynamics, training routines and general advices to handposistions are very useful to me.
That is why I recommend everyone who wants to learn an instrument later in life: just do it - no matter how old you are! You will not have the speed of a 8 year old, yes. You will be even slower than your children are (*caugh) - but hey: there are decades full of the beauty of music ahead of you. It is never to late ;)