It can be real in (some) instances however the majority of the time a person is labeled with it is because they are (not conforming) or behaving the way another person thinks they ought to.
Just recently I asked the relationship question: "Is there a real difference between (fear of commitment) and (refusing to settle)?
In my opinion they are two sides of the same coin. Neither person is moving forward to commit to anyone! Nevertheless people often state someone has a "fear of commitment" if this person does not want to commit to them!
Most truly creative people have some elements of the "Peter Pan Syndrome". They don't believe things have to be done the way they've always been done. Mavericks or those who dance to their own music are also often accused of having the "Peter Pan Syndrome".
To some extinct a person might label the "baby boomer" generation with the "Peter Pan Syndrome". One of our mottos is:
"I refuse to grow up!"
We were the first generation in our 20s to give children permission to call us by our first names instead of insisting they call us Mr./Ms.
We rebelled against "the establishment", created the hippie and "free love" movement, counter drug culture, pushed Rock & Roll, Motown, Disco, and Funk music to the forefront, created the personal computer, video games, and the various slogans;
"60 is the new 40", "50 is the new 30" and "40 is the new 20".
Unlike previous generations who resigned themselves to getting old, baking cookies for grandchildren, or playing checkers on the front porch, we run or workout in the gym, women in their 50s still wear mini-skirts, get plastic surgery and buy dozens of products that enhance a youthful appearance. Instead of looking forward to retirement we're launching new businesses or pursuing second careers! Although we make up the largest age group in the U.S. AARP membership has declined. The Rolling Stones are in their 70s and still tour playing Rock & Roll music!
One could easily argue all of the aforementioned behavior are elements of the "Peter Pan Syndrome". Life is a personal journey.
Each of us gets to live our life on our own terms!