My roof has bad streaking on it and is over 20 years old. Will my insurance company cover the cost of a new roof?

Highly unlikely. Sounds like wear and tear which is generally not covered by home owner's insurance.

No, it will only replace damaged roofs

No, it will only replace damaged roofs

And even that depends on the reason for the damage.

Streaking is a cosmetic problem and not a structural problem causing water intrusion. No, they won't cover this. When you do replace your roof you need to address what pieces of metal are leeching the streaking and have the metal properly addressed so it won't streak onto your new roof.