ONE HUNDRED games and about four and a half years separates Joel Selwood and Luke Parker, but when you stand the two midfield stars side by side, there's not much else between them.

On Saturday night, the Geelong captain plays game 200, while the younger Sydney Swan brings up a century, and they'll do it on the same patch of turf at Simonds Stadium. 

The comparisons between two of the best in the competition are obvious, both men played in a premiership team, won a best and fairest and registered the ton of senior games before they turned 23 years of age.

So what puts Selwood and Parker on a tier above most players in the league? Tom Harley seems the perfect man to ask.

The former Cats skipper welcomed Selwood to the club back in 2006, and he's now getting a close up look at Parker as the Swans' general manager of football in Sydney.

In an exclusive interview with AFL.com.au, Harley says there's no secret behind the pair's early success. 

"Anyone who can play in a premiership straight off the bat, and win a club champion award before they play 100 games, you're talking about rarified air," Harley said.

"I think a lot of people could make the easy call and say that Joel and Luke happened to be in the right place at the right time at a good club.

"But I think what is clear is that both players have contributed significantly to making their already great clubs better.

"I think what they both do is they sense the moment as young players, they sense when the team needs a lift, needs some grunt around the ball, and they play at a high level consistently. 

"Luke's got a bit of a way to go to be a great of the game because he's only played 100 games, but he's certainly tracking in that direction." 

Selwood came into the AFL with the likes of Matthew Scarlett, Darren Milburn and Jimmy Bartel to learn from, while Parker's mentors at the Swans included Jarrad McVeigh, Jude Bolton and Adam Goodes; a cast of all star leaders.

But Harley says the quality of players such as Selwood and Parker should be measured by the affect they have on senior players already entrenched in the system. 

"There's a pretty well told story about when Joel came to Geelong, he had an air of confidence about him without a hint of arrogance," Harley said.

"It's a real confidence and sense of belonging at this level and there's a presence about those sorts of players when they come in. 

"I wasn't here (in Sydney) at the time, but Luke obviously did the same because he played in a premiership really early, which is a great effort. 

"With any sort of player like that who is highly regarded and part of the leadership group at a really good club at a young age, they're good people first and foremost. 

"They train and prepare the right way, they build strong relationships, and they play well.

"If you can tick those boxes you're going OK, but they in their own mind they won't think that they've ticked every box.

"You've got to be a self starter, you've got to always look for ways to get better, and that in itself is a really good lesson for younger players." 

If ever there was a one-on-one, old-fashioned battle the fans would want to see, you get the feeling that Selwood and Parker would be right up there. 

They're a couple of courageous, selfless blokes who live and breathe a 'win at all costs attitude', and Harley thinks – even though they might not say it publicly – that the two warriors will relish a battle in round 19.

"I'm sure they'd have a very high mutual respect for each other, and I would imagine knowing both of them, that it won't be lost on them that they're sharing a significant milestone together," Harley said. 

"They might shake hands at the start, if players even do that theses days, then go absolutely hammer and tongs, but I can guarantee they'll shake hands at the end.

"Whichever way the result goes, they'll give a tip of the hat to each other and say well done on the milestone."

Joel Selwood v Luke Parker - their first 100 games

* inclusive of Selwood's 100th game in R8, 2011 v Collingwood
** from 82 games to end of 2014