The Denver Broncos quarterback faced the AFC South side 19 times during his time with the Indianapolis Colts, but has not played them since 2010.
The 37-year-old told the team's website: "Oh it seems like a long time ago, 2010. They have some new players so they have new schemes, different coaches. Still getting to know them.
"Yeah, I guess just when you have a new defensive coordinator and a team that you didn't play last year, a team that you're not playing twice a year.
"2010 is a number of years ago. And it's still early in the season so it's still hard to know exactly what you're going to get."
The Jaguars sit bottom of their division with no wins so far this year, while the Broncos are undefeated.