I think for a girl the best marriage age is from 21 st to 24th.By this time one should have completed her studies or will be completing studies.Also she would have enough maturity to deal with a boy.
For boys the best age is from 24th to 27.This is because he will have attained a stand then by entering some jobs.Without an employment marrying will be stepping to hell.Also the age difference between the couples should be 4to5 years for enjoying the married life at its best for a long duration.