The purpose of life is to find the purpose of life. More specifically, your life. No one else matters. Their purpose of life is their business. They can and will answer this question differently from you. What's more, the way you answer this question will be different every time you ask it, because what is important to us is never precisely the same from day to day; certainly the way we express the answer changes, evolves, deepens.
What does this tell us? That the elusive answer to that eternal question is no answer at all, because it is so mutable? Does that mean we are left with only the question, unyielding, unchanging, while the multitudinous answers dance around it, mocking us? We mock ourselves in pursuing this quixotic quest. Why not let it go? Because we can't. It's our purpose to try to answer. Our very existence on this earth is testament to the fact that the question is on the table.