My DS7 started Suzuki piano at 5 - the year before kindergarten for him (he has a fall birthday). He's been taking a bit over 2 years. He was asking to do it. For him it has been WONDERFUL. And believe me, he has plenty of days he doesn't want to practice. I sit down with him and don't allow anyone or anything to interrupt us when we're practicing. I throw in lots of games and incentives, etc. Many performance opportunities (ie showing off) help a lot. And I think you just need to know if you start young, parents need to be very involved and consistent in my experience. And I like who talked about being "good enough". We take a day off every week and usually have 1 or 2 lighter practice days. Sometimes if we're preparing for something or his teacher is running a contest, we have some heavier weeks. Make sure you find a teacher who really "gets" and clicks with your child.
I also grew up taking Suzuki violin and my brother took Suzuki piano. I personally had a wonderful Suzuki experience. DD4 is likely to start Suzuki violin (hopefully) this fall. She seems more ready than DS did at 4 - not quite as squirrelly and she's asking to start now as well. We have a waiting list where we take lessons - it's a very popular program.
I also highly recommend reading Nutured by Love.
Good luck!
