This question is interesting and important because it affects many people in different segments of the society.
If you have been using the wrong date of birth in your documents and now wish to start using your real age, the most legally acceptable way to rectify the anomaly in Nigeria is to depose to an Affidavit in court or before a Notary Public, stating that fact. In doing so, depending on the facts and circumstances of each case, you must state that you have been using the initial (wrong) date of birth unknowingly and innocuously with the belief that it was the right date, having been so informed earlier in life.
It is important you also state that the new date of birth was availed to you after your attention was drawn to new information brought from a very reliable source.
After deposing to the Affidavit, you are expected to a make a publication of the error in a newspaper (preferably one with a regional or national circulation) urging relevant authorities to disregard your old date of birth and henceforth be minded of your new date of birth.