21. (Total Score: 14 points) Subproblem 1: 6 points, Subproblem 2: 8 points.\\
Given that the sum of the first $n$ terms of sequence $\left\{ a _ { n } \right\}$ is $S _ { n }$ , and $S _ { n } = n - 5 a _ { n } - 85 , n \in \mathbf { N } ^ { * }$ .\\
(1) Prove that $\left\{ a _ { n } - 1 \right\}$ is a geometric sequence;\\
(2) Find the general term formula for the sequence $\left\{ S _ { n } \right\}$ , and find the minimum positive integer $n$ such that $S _ { n + 1 } > S _ { n }$ .