In my opinion, any age is a good age to start piano lessons! :)
It really depends on the teacher.
Children a few decades ago usually waited until they were 6 to 8 years-old before beginning lessons. However, we have learned that there are benefits to starting at a younger age.
Young beginners are enthusiastic, and can begin enjoying music and establishing a practice routine long before other students are just starting lessons.
I recommend that students ages 3 to 5 years-old have a readiness assessment or at least a trial lesson before beginning lessons, and that they study with a teacher who ENJOYS working with these ages. Otherwise, you may want to wait until the child is reading well.
Try to have at least a few names and communicate with your potential teachers on the phone or via e-mail or even in person before deciding if you are a good match.
Link to MTNA's Choosing a Music Teacher
The cost varies from teacher to teacher. There are many factors that affect lesson prices, including; teacher qualificatons, experience, location, space rental fees, etc.
In the Houston area, expect to pay anywhere from $14 to $75+ per half hour lesson depending on the teacher.
Most teachers require a real piano, even for beginners! Although keyboards have come a long way, they still cannot help the student build the finger strength and independence they need to succeed.
Also, a keyboard may have fewer keys and this creates a huge problem. Most piano teachers include methods that encourage using the entire range of keys right from the start, so students learn to read well and play comfortably anywhere on the instrument.
I personally do not turn students away if all they have is a keyboard, but I do highly recommend they find an acoustic piano at school, church, neighbors house, relative, etc. to play as often as possible.
You might think this is a good idea. But, remember that students are inspired both by the sounds they produce themselves and their success at the instrument. You want them to spend quite a bit of time practicing at home on this instrument. So, remember:
If you have a piano that doesn't sound so great, then neither can your child.
If you have a piano that doesn't work so great, then it will be harder to play.
I recommend that you get the best piano you can afford - right from the start. You will ALL be glad you did!
Only if they have to do this. I don't recommend it. Even students taking lessons a few years apart may see the second one easily playing by ear or experiencing more frustration.
Hopefully, the teacher will be well versed in several methods and choose one that will work for each student. It is tough enough to learn to play piano without undertones of sibling competition, whether it is intentional or not.
EXCEPTION: Friends who attend a group class seem to do just fine if they have the same method book. But, they should have some pieces that are just their own from time to time.
MTNA is the Music Teachers National Association, and there are many affiliates such as the Texas Music Teachers Association etc. They are not associated with the public school system associations, but may coordinate or even offer joint events with them at times.
These associations offer teachers and students various educational and performance opportunities.
The National Federation of Music Clubs has local, state, and national chapters. They promote many events to encourage students and teachers to advance their skills and share their music. NFMC groups tend to add a social aspect to meetings and have events for non-competitive students as well.