Answer
$\Delta t_{\circ}=0.80 y$
The final age is $35+0.8=35.8\ years$
Work Step by Step
We know that
$\Delta t=\frac{d}{v}$
But we also know that
$\Delta t=\frac{\Delta t_{\circ}}{\sqrt{1-v^2/c^2}}$
$\implies \frac{\Delta t_{\circ}}{\sqrt{1-v^2/c^2}}=\frac{d}{v}$
This can be rearranged as:
$\Delta_{\circ}=\frac{d}{v}\sqrt{1-v^2/c^2}$
We plug in the known values to obtain:
$\Delta t_{\circ}=\frac{25.3ly}{0.9995c}\sqrt{1-(0.9995)^2}$
$\Delta t_{\circ}=0.80 y=9.6 months$
Thus the final age is $35+0.8=35.8\ years$
