The 34-year-old is coming off another impressive campaign at Paris Saint-Germain, scoring 50 goals in 51 appearances in all competitions.
Ibrahimovic, who is preparing for Euro 2016 with Sweden, is reportedly close to sealing a move to Old Trafford as his next destination.
The striker said he was still getting better despite approaching his 35th birthday.
"Whether I am 34 or 35, I have never had a better season than this," Ibrahimovic told the Daily Mirror.
"I am still developing as a player, but it is all about getting the job done – and I do a hell of a job."
Ibrahimovic said he had proven he was still capable of performing, having helped PSG to four straight Ligue 1 titles.
"I have proved that I still have a young mind," he said.
"The mental part is 50 per cent of football and that has never been a problem for me."
Ibrahimovic and Co. will take on Belgium, Italy and the Republic of Ireland in Group E at Euro 2016, which starts on June 10.