Just as there isn't too old to start singing, there's no such thing as too old to start a singing career if you really want one. Country superstar Sheryl Crow didn't have a hit single until she was 32 years old. This depends on gender, but an average is teenagers up to their early 20s. While this knowledge shouldn't stop you from starting a career later, it should also stimulate you if you're younger and thinking about delaying it.
If you have talent and determination, the sooner you start the better. The truth is that you are never too old to start making music. The only exception is if you want to be a pop star and get a contract with a major record label. If it's not you, then age is no barrier to success in the new music industry.
If the child enjoys music or sings on radio or television programs, this is a good indicator that he is ready to start learning to sing. The reason I'm asking is because the latter is totally possible and realistic for almost anyone of any age. We all have to start somewhere, and overcoming the mental block of “I'm too old to do this” opens the door to so many different possibilities in life. Because of this, it could be quite daunting for talented singers who consider themselves late to enter the music scene.
When you look at today's pop stars, you might feel like it's too late to go on stage. However, the human voice continues to mature throughout life, so students of any age can benefit from singing lessons. It could be more difficult for competitions, but as a singer if you start at 17 you will still sound great by the time you turn twenty, which is going to be very good. The best age to learn to sing depends less on physical maturity and more on factors such as self-motivation, available practice time and ability to concentrate.
You want to at least try to start singing classes now, but if your parents say no, then what you're proposing is also fine and 17 would be a good age to start just singing in general. Students starting singing classes should be socially mature enough to focus on the classroom and follow the training of their instructor. Starting later in life can be beneficial for those who have studied and practiced their trade, gaining musical knowledge and working hard. I started classes at age 16 and felt quite early compared to many of my classmates who didn't start classes until college.
I personally started my classes around the same time as you, it was December of the year I was 14 years old. With over 25 million albums sold, Grammy nominations, Guinness World Records, Endless Awards, performances for royalty and some of the biggest TV shows in the world, being a 'late' has brought me acclaim. Whether you want to start singing alone or start a band, it's a great way to get into the local music scene. In fact, for some microgenres, being older could be an advantage because the listeners are older.