First of all you should know the meaning of life. The life is nothing but UNWANTED BIRTH AND UNAVOIDABLE DEATH as the Life is short, you have to make it sweet by all means.
I learnt that not only for marriage, to lead life fully well, you should be economically independent (i.e., a job to earn money which shall be enough for 30 days x 365 days) and get knowledge or training about self management, home management along with money management.
If you make yourself a good observer, it is enough to make you a knowledgeable person.
Any boy above 21 years of age with financial independence and any girl 18 years of age can immediately get married and start their life if they are having sufficient responsible attitude with sincere commitment.