The 38-year-old was elected to the position in February.
"Looking back on my career, I wish I had the head on my shoulders that I have now," he told BBC Radio 5 live.
"Ability will take you so far but the mental side is more important. That knowledge I can pass on."
Flintoff, who embarked on a television career after retiring from cricket in 2010, played 79 Tests and 141 one-day internationals and was key to England's Ashes successes of 2005 and 2009.
However, he also made the headlines for his off-field behaviour, including a drunken late-night incident in St Lucia involving a pedalo during the 2007 World Cup.
Since retirement, the former Lancashire player has spoken frankly about depression.
"I am more self-aware and know more what makes me tick, how I think and all those things," said Flintoff. "If I had known that when I was 25 I would probably still be playing now.
"As a young player, it is about learning about yourself, how to be a professional sportsman. The sooner you can do that, the sooner you will start performing.
"One of things I would encourage is for them to be open. In my days, if I'd spoken about it in a dressing room, I would have been laughed at."
Flintoff said he may consider taking his coaching badges, having shunned the game for "three or four years" after retiring as he was "searching for a long time for something to replace cricket".
In his role with the PCA, Flintoff says he will look to help older players facing a similar situation.
"You want to put all your energy into being the best you can and play as long as you can and you neglect what is going to happen next," he said.
"Sometimes you get so consumed in cricket and the importance of it that it just takes over everything."
One of the key programmes run by the PCA is its work on mental health and wellbeing for past and present players through the Mind Matters series.
Ex-England all-rounder Andrew Flintoff believes he can help young cricketers with the mental side of the game, in his new role as president of the Professional Cricketers' Association.