Howell, 28, pointed to last Sunday's Masters Tournament victory by Immelman, 28, and the PODS Championship win by O'Hair, 25, in March, and said he believes his best days are ahead.
Howell shot 2-under-par 69 on Saturday at the Verizon Heritage. He is tied with three other golfers for 10th place going into today's final round at Harbour Town Golf Links.
"I just think it's difficult to win (on the PGA Tour)," said Howell. "There's 156 guys each week, give or take a few, that can win the golf tournament.
"But, you know you see Sean O'Hair won this year. You see Trevor (Immelman) won the Masters. I just think it takes a bit of time to find your routine and what works for you. I think that's why golfers hit a lot of their peak and their stride in their mid-30s."
Howell tied for 19th place at the Heritage in 2002, the last time he finished the event. He missed the cut in 2003.
Last week, Howell shot 4 over at the Masters and missed the cut.
"Scheduling is tough," he said. "This year, I had a little more time off before the Masters and, consequently, this is only my third (tournament) in a row, so it fits in really well.
"I love the (Heritage) golf course. It's a lot different than anything we play for the majority of the year, but I think a lot of players like that. I think a lot of players like this place. It's definitely a place that I definitely want to keep coming back to."
Howell's best finish this season was in January at the Mercedes-Benz Championship in Hawaii. He shot 13-under 279 and tied Justin Leonard for eighth place.
"The game is getting there," he said. "Sometimes, it just takes a shot or two, a round or two, here or there to see yourself get going. I'm getting a lot closer."
Reach Noell Barnidge at firstname.lastname@example.org