Let's solve the problem step-by-step.

Let:
- \( F \) be the father's current age.
- \( S \) be the son's current age.

According to the problem:

1. The father is now twice as old as his son:
\[ F = 2S \]

2. Sixteen years ago, the father was six times as old as his son:
\[ F - 16 = 6(S - 16) \]

We now solve these equations.

From the first equation:
\[ F = 2S \]

Substitute \( F \) in the second equation:
\[ 2S - 16 = 6(S - 16) \]

Expand and simplify:
\[ 2S - 16 = 6S - 96 \]

Rearrange to solve for \( S \):
\[ 2S - 6S = -96 + 16 \]

\[ -4S = -80 \]

\[ S = 20 \]

Using \( F = 2S \):
\[ F = 2 \times 20 = 40 \]

So, the father is 40 years old and the son is 20 years old.

The correct answer is A. 40 years and 20 years.