Though Steven Jackson isn't suiting up for a St. Louis Rams season opener for the first time since 2004, that won't diminish raised expectations for a team that hasn't made the playoffs since his rookie year.After turning 30, he would have been considered a senior citizen on the league's most youthful roster, anyway.The Arizona Cardinals are counting on the experience of new coach Bruce Arians and veteran quarterback Carson Palmer to help key their turnaround, beginning Sunday in St. Louis.Jackson opted out of the final year and 7 million remaining on his contract to sign with Atlanta, leaving as the Rams' all-time leading rusher with a streak of eight consecutive 1,000-yard seasons.His departure, while disappointing, hasn't dampened the enthusiasm of a St. Louis team that won four of its last six to finish at 7-8-1. Coach Jeff Fisher expects an even better year from the Rams, who added tight end Jared Cook and offensive tackle Jake Long to help quarterback Sam Bradford."One would assume that we'll just continue to get better," Fisher said.General manager Les Snead thinks so, too."Now is when you've got to learn grit," Snead said. "They're going to know we're coming."St. Louis' 53-man roster has an average age of 24.98, the lowest in the NFL for the second straight season. Daryl Richardson, 23, replaces Jackson as the starting running back after averaging 4.8 yards per carry in a backup role as a rookie. He beat out last year's second-round pick Isaiah Pead, who is suspended for Week 1 after violating the league's substance abuse policy.Add receiver Tavon Austin, the No. 8 overall pick, and the Rams boast a young, potentially explosive offense despite losing Jackson."I see us being so young as an advantage in some ways," Richardson said. "We've got room to grow, room to get better. We're working hard because we really want it."There's no youth movement happening in Arizona, where the 60-year-old Arians received his first permanent NFL head coaching job after a successful interim stint with Indianapolis in 2012.The Cardinals, who started 4-0 before dropping 11 of their final 12 last season, acquired the 33-year-old Palmer from Oakland to help settle a quarterback situation that has been in limbo since former Ram Kurt Warner retired."This is a cowboy movie," Arians said. "With two old guys, this is our last rodeo in the desert."Palmer, who threw for 4,018 yards and 22 touchdowns last season, said the new offense has been tough to grasp, but he's counting on star receiver Larry Fitzgerald and others to help as everyone makes the transition.Arizona, which finished last in the league with an average of 75.3 rushing yards per game last season, also signed Rashard Mendenhall from Pittsburgh to be its starting running back after he was plagued by injuries in 2012.They'll all look to help improve a Cardinals offense that ranked last in the NFL with 263.1 yards per game and tied for the second-most turnovers with 34."We have smart football players on this offense," Palmer said. "Combine that with athleticism and speed and experience. You look at a guy like Larry's experience and his catches and his touches in games, I'm as excited and as optimistic as ever."Bradford feels the same way. This is the first time the former No. 1 overall pick isn't learning a brand new scheme, as offensive coordinator Brian Schottenheimer returns for a second season."I thought we had a really good training camp," Bradford said. "I thought we did some really good things during the preseason when we were on the field, and now it's full steam ahead getting ready for Arizona."The Cardinals may be adding a new wrinkle to their scheme, as cornerback and return specialist Patrick Peterson has been taking reps with the offense. Arians believes he can surprise opponents by using Peterson, who said the team has instituted roughly 60 plays for him."(Fitzgerald) was kidding me," Peterson said. "He said, 'Technically, you're our fifth receiver.'"The Rams' defense ranked 14th with an average of 342.6 yards allowed last season, and it will look to improve on that number with help from rookie linebacker Alec Ogletree, the club's first-round pick.Fellow former SEC competitor Tyrann Mathieu is expected to see plenty of snaps in the Cardinals' secondary after being selected in the third round despite being kicked off the LSU team prior to last season.St. Louis won both meetings with Arizona last season, 17-3 on Oct. 4 and 31-17 on Nov. 25.