The 17 year-old has been superb for Barca this season.
"Now it becomes easy to say, of course I see him as the best winger in the world," Lewandowski told B/R Football.
"But of course he is 17 years old. A football career is so long, sometimes it's not important how you start, what's more important is how you finish or how will be the next years, not two or three years but the next 10-15 years. And in 15 years he will be 32."
Lewandowski also commented on the new generation in general.
"When I see the next generation... they have a huge challenge for themselves, in social media. One day you are the hero, but the next day you are on the ground.
"I wish him (Yamal) to be strong for the long career, and it doesn't matter what the people say now, or what the people will say, he stays on the ground and thinks: 'okay, it's part of my life , the football that I want to enjoy, I want to give the fans a lot of joy'."