Justin Smith will turn 35 on Sept. 30, so it's obvious his days in the NFL are numbered.He's signed through this season and next, so it's possible that 2015 will be his last in a 49ers uniform.Though Smith is ancient in the world of professional football, the Niners' defensive right end in their 3-4 defensive alignment has remained a force, and likely will be a key to San Franciso's defensive success in 2014. In the NFL Network's recent countdown of the top 100 players in the league, Smith came in at No. 69. That's down from No. 29 the year before, yet still among the best of the best. - Niners' Carrier Getting His Chance to Impress"You can ask anybody that's blocked him, and that's probably the first thing they'll say about him, he's a strong cat," said Rams offensive tackle Joe Barksdale. "Really, really strong. I don't know how he got that strong."And, said Barksdale, he's relentless."He's an all-day sucker," Barksdale said. "Whether they're up by 30 or down by 30, he's going to keep coming."Added Buffalo Bills tackle Chris Williams: "He's one fo the few players I've ever played against who you know what he's going to do, and you still have a hard time stopping it." - Niners'...