You have your point, but respect should go both ways

I believe the original poster is rightfully upset. According to him, the old couple complained to the management just days after moving in without even trying to communicating with him. But I do believe it will be helpful to resolve this matter by first trying to have a friendly conversation with the old couple. Maybe a mutually agreed time period for his kid to practice piano can be the best solution. However, if people are unreasonable, which is not uncommon among elders, there is no reason for you to bend backwards just to please them.