Mickey and Minnie just bought a zero coupon bond for $$634\mathrm{.}84,$ but they cannot recall when it matures. The yield to maturity equals $4\mathrm{.}1\%.$ Can you help Mickey and Minnie? The bond's face value is $$1000.($Assume annual discounting$)($Enter your answer in years and round to $2$ decimal places.$)$