To answer the question, you need to solve this equation


     = 2,


fOr t, where t is the time in years.


Take logarithm from both sides


     = log(2),


simplify 


    2t*log(1.0632) = log(2)


and get  


    t =  = 5.66 years.


So, 6 (six) years is enough to double the starting principal.