Step 1: Evaluate the squares.
\[
5^2=25,\;
6^2=36,\;
7^2=49,\;
8^2=64,\;
9^2=81,\;
10^2=100.
\]
Step 2: Find the sum.
\[
25+36+49+64+81+100=355.
\]
There are
\[
6
\]
numbers.
Step 3: Calculate the mean.
\[
\text{Mean}
=
\frac{355}{6}
=
59\dfrac{1}{6}.
\]
Step 4: Final conclusion.
\[
\boxed{59\dfrac{1}{6}}
\]
Hence, the correct option is \(\boxed{(A)}\).