I think this is an interesting language point. 让 means let, and in some circumstances, make, as in "when you talk that way, it makes me feel bad." In this circumstance, I think there is a better verb. Consider this example: "小李最近总是不开心，原来他是被父母逼婚。Li not happy recently, as he was forced to marry against his will." Alana is being forced to play the piano against her 5 year old will; I think 逼 (bi1) is the better word.

wo3 wu3 sui4 shi2, ma1ma1 rang4 wo3 tan2 gang1qin2. [email protected]/ skype: reina.zhang1

在我五岁的时候， 我妈妈让我学钢琴。 I feel like that "在" is better than "当”， is more spoken. "play piano" here means not only "弹钢琴” but also "学钢琴"， since you were five-years -old girl and was made to "play" piano. So I feel like that 学钢琴 is a proper expression . Any questions, don't hesitate to ask me. ^^)

当我五岁的时候，我妈妈让我弹钢琴。I think this is the right answer.:)

我5岁的时候，妈妈逼我学钢琴。