The 33-year-old scored his 100th and 101st goals in Saturday's win over Coventry and is pleased his dedication to fitness is continuing to provide rewards.
He said: "It's a nice achievement to reach the 100 league goal mark and there are a few left in me.
"I look at people like Ryan Giggs and I think I can keep on going like that, maybe for another four years. I feel fitter than I've ever done."
Gray has also credited the tactics of Barnsley boss Keith Hill, which have provided him with more goalscoring opportunities.
He said: "The new manager has been fantastic. He wants us to play football and we have been passing some teams off the park.
"His style has helped me, as I'm a big target man. We are getting lots of balls into me - it suits the way I play."