How long you keep personal financials is a personal decision, but it is recommended that you hold on to your financial records as long as the IRS can audit you. Five to seven years is recommended, but it could be longer depending on your profession and role in business.

Speaking in regards to financials needed to get approved for real estate finance, the longest history I have had to document is three years. Typically lenders want to see two years, sometimes one. Three year documentation was required due to large interest earnings from various portfolio positions which was required to validate history and chance of continuance. If this is not your situation expect two years.