I am turning 18 next month.?
Like Adhaar, PAN etc achieving age of 18 has nothing to do with your passport. EDIT: I came to know 5-year validity passport is issued to those below 18, and 10-year for above . By my experience, what matters to airlines is they charge you full ticket as adult if you reach age of 12 as per your passport, half ticket for below 12, and 10% of ticket fare for infants.