There is no exact time frame for when a person must file taxes unless his income is above a certain threshold. Consult the tax forms for the appropriate year or the IRS website for information on whether income is high enough to require filing.
It is recommended to file a tax return every year to avoid fees and penalties if the filer is likely to owe money. The IRS is more likely to search for a company or business owner rather than an ordinary citizen because businesses are more likely to owe taxes.
The IRS has recommended filing every year whether a person owes taxes or not because the IRS sometimes owes him money. After three years a tax refund is unable to be claimed.