I guess I have to dig out my compound interest formula :P
$${\mathtt{A}} = {{P}{\left({\mathtt{1}}{\mathtt{\,\small\textbf+\,}}{\mathtt{r}}\right)}}^{\,{\mathtt{n}}}$$
Where A is the amount,
P is the original value and,
r is the rate and
n is the number of compound periods.
So, lets fill out the stuff we know.
$${\mathtt{1\,000}} = {\mathtt{500}}{\mathtt{\,\times\,}}{\left({\mathtt{1}}{\mathtt{\,\small\textbf+\,}}{\mathtt{0.06}}\right)}^{{\mathtt{n}}}$$
This might not be correct but I believe it would be rearranged as so,
$${\mathtt{n}} = {\sqrt{{\mathtt{500}}{\mathtt{\,\times\,}}\left({\mathtt{1}}{\mathtt{\,\small\textbf+\,}}{\mathtt{0.06}}\right)}} \Rightarrow {\mathtt{n}} = {\mathtt{23.021\: \!728\: \!866\: \!442\: \!676\: \!4}}$$
Thats how many compound periods it would take.
To find the answer in years divide by the amount of compound periods in a year.
Good luck! 