He revealed what he considers to be the Northern Ireland international's secret to success during his first two top-flight seasons.
"Throughout the season the vast majority of the squad have had moments where they've been good and important for the club and for the team," said Clarke to the WBA website.
"Almost everyone has made a good contribution but if you're looking for consistency over a season then Gareth is a stand-out for me. It just goes to prove age is no barrier.
"If you're hungry enough, fit enough and good enough you can be a top player. It doesn't matter when you do it. He got his chance late to play in the Premier League and he made the most of it. It shows in his performances.
"He's a person who looks after himself well. He looks well, he eats well, he hasn't got a pick of fat on him. He's good, he works hard every day in training, he trains the way he plays - at 100 per cent.
"He doesn't shirk on training, he doesn't protect himself - he puts everything in. When you have players like that they tend to have longer careers.
"He's probably trained 90 per cent of the sessions this year, which is fantastic for any player, never mind a player everyone keeps saying is a little older.
"You're only as old as your body feels."