Lynch isn't, nor is Barber, but Portis, Johnson, LDT, and Westbrook are on the way out. Westbrook is in the best position because he started late, but the other 3 have some serious mileage on them. LDT, Johnson, and Westbrook will turn 30 in 2009, and Portis has been ridden very hard behind a mediocre offensive line in Washington. Portis and LJ have the biggest disadvantages because their lines are much weaker than they were a few years ago, but LT has been ridden very hard up to this point and has been very lucky with injuries. I'll say that by the start of the 2010 season, 1 of those will be off the team completely after injury, 2 will be splitting time, and 1 will have another year as a starter. With the injuries and the quality coming from college, no team needs to be playing 30 year olds with 6-10 years of starting experience.
Time is running out isn't the same as on their way out soon. You have generally 3-5 years as a starter before you're really slowing down. Thomlinson is lucky because he has the best run blocking OL in the world which will prolong his run a little longer, but especially with backs, you're generally not improving after 3-5 years.