At 25, Dolphins cornerback Jason Allen isn't old. Not by the NFL's standards. And certainly not by society's standards.

Yet these days, as Allen grinds away at his fourth training camp since being drafted 16th overall in 2006, he can't help but feel like the grizzled veteran as he scans Miami's defensive backfield. Vontae Davis. Sean Smith. Chris Clemons. All fresh-faced rookies.

``It's crazy how the time goes by so fast,'' Allen said in a quiet, monotone voice. "I'm going into my fourth year in the league. Seeing Vontae, Sean and Chris, you think about how that was me just a few years ago. I tell them how it goes by so fast.''

If the nostalgic comment seems to imply some strange sense of conclusion -- like a senior in college reflecting on his past four years -- that wasn't Allen's intention. This is not the end for him. He is likely to again make Miami's 53-man roster.

His focus is there, too. But Allen no longer has that same, innocent optimism in his voice that once suggested he would settle for no less than stardom. He talks with a concise simplicity, leaving little room for the criticism that has followed him during his career.

``I'm really trying to focus on my position, trying to really go into the details of it,'' Allen said. ``It's been good for me.''

After all, as Allen will tell you, there's very little he hasn't heard off the field. And very little he hasn't tried on it.

In the past three seasons, under three coaches, Allen has been switched from safety to cornerback to safety to cornerback to safety and back to cornerback. Oh, by the way, he also now is playing another new subset role as a nickel back.

How is he handling the latest transition?

``It's something new for me because it's the first time I've ever done it,'' Allen said. ``The more you know, the better it is for you. I'm actually enjoying playing the nickel. It's the first time I've done it, but I'm enjoying it.''

Plenty have blamed Allen's constant shifts between safety and cornerback on his inability to vault into a steady starting job. Nick Saban and Cam Cameron cited the problem as the reason for his slow development.

Even coach Tony Sparano has done it.

``We moved him to a new position, and we've asked him to do some other things out here right now in the nickel [package],'' Sparano said Thursday. ``So, I mean, I've started to see some things slow down for him right now, and he's reacting.

``You're starting to see his athleticism.''

As frustrating as the monotony of those comments might seem, Allen's ability to play many roles might be helping to extend his career.

Allen is right: The more you know, the better it is. That especially is true under the current coaching staff.

Versatility is one of Sparano's favorite qualities. With the ability to play multiple roles -- and more importantly, his success as a special teams standout -- Allen should have a secure place on the roster.

Of course, Allen's role still won't be the one he envisioned when he first arrived in the league in 2006. The arrival of Davis, Smith and Eric Green has buried him further on a depth chart that has not been kind to him over the years.

But he has a role. Many roles, to be precise. So Allen will continue to move forward with a simple goal in mind: He's in Miami to help the team, playing whatever position required of him.

``Learn how to be a professional,'' said Allen, when asked what advice he would give the rookies. ``That's the biggest thing.

``In college, the only thing you worry about is going to class and playing football. But here, you really have to pay attention to details, study and be really dedicated.

``You have to be professional on and off the field.''