De Jong will move to La Liga champions Barca at the end of the season after agreeing a transfer worth €86million in total.
The 21-year-old midfielder attracted interest from Europe's biggest clubs, including French giants Paris Saint-Germain, before opting for Barca in January.
"There are a lot of special players when you look around the world at the moment, but he is obviously very special. Absolutely," Olsen – who won two Eredivisie titles and the KNVB Cup during his three-year spell with Ajax in the 1980s – told Omnisport.
"The calmness, we can't even say the experience because of his age, but he looks like he's very experienced and that takes a very special kind of player."
Olsen continued: "Barcelona will always be at the top, together with Real Madrid. They're kind of regenerating their team. Messi is still doing his job. It's amazing when you think about the years he has been doing that.
"Barcelona are a great club to go to, no doubt about it."
De Jong has scored three goals this season, while the Netherlands international played a key role as Ajax stunned Real Madrid in the Champions League round of 16 last month.