en_tn_condensed/psa/061/006.md

You will prolong ... many generations

These two clauses have similar meanings. The idea is repeated for emphasis. (See: rc://en/ta/man/translate/figs-parallelism)

You will prolong the king's life

"You will extend the king's life" or "You will cause the king's life to last a long time"

his years will be like many generations

Here "years" refers to how long the king will live. Alternate translation: "he will live for many generations" (See: rc://en/ta/man/translate/figs-metonymy)