"He has some quite considerable time left on the contract but he's been brilliant," said O'Neill. "When we signed him from Watford we paid a lot of money 'for' him but we didn't pay a lot of money 'to' him and that's fine.
"It was still a lot of money to pay for him, but at the end of the day he might be worth three times that now. It's all relevant now.
He was voted in the PFA team and that's a big compliment. The progress he has made in the time that he has been here is astounding."
O'Neill had no doubt that Young would come to the fore at Villa Park and make a huge impact in the Premier League.
"I had seen enough of him to know that he would come through.
"He took a bit of time to settle, started off quite brightly and then went into a bit of a lull, then started to find it at the back end of last season and then carried it right through the summer and it's gone on."