Going by memory mango trees start giving fruit when they are between 5 and 8 years old according to cultivar and growing conditions. Nursery-grown trees are often grafted and these will start to give fruit after 3-4 years.
Mind that flowering, like in most Anacardinaceae, is stimulated by "cool" nights, meaning nightly temperatures of 20-15°C (high to low 60's): in countries like India and Thailand, were mangoes are extremely widespread, a cool spell often means an extremely abundant mango crop in the year as flowering is great stimulated.
