Former number one Martina Hingis is not impressed by the current crop of young players whose main focus is on hitting harder, rather than developing an all-round game, the Swiss veteran said.
Hingis became world number one in 1997, at the age of 16, and won her first Australian Open, Wimbledon and US Open singles titles that year.
She won 40 singles trophies before her initial retirement at 22 and returned for a year in 2006, making a full return in 2013.
"The education, in tennis terms, was better," Hingis told the Times.
"The age rule was different then, now it's stricter (the WTA limits the number of tournaments a player under 18 can compete in). Today, everyone just hits hard, harder and hardest.
"There are a lot of players who don't really strike me. They have a good match or two but I'm like 'OK, is there something more in this player that I could see is going to be a future champion?'"
The WTA introduced age eligibility rules in the 90s, which have since been updated and enforced more strictly to prevent players from burning out and retiring early.
Youngsters rarely make an impact in the latter stages of big events these days, with Latvian Jelena Ostapenko being the exception, winning the French Open two days after her 20th birthday and progressing to the fourth round at Wimbledon.
Ostapenko will face Elina Svitolina in the fourth round on Monday while Hingis, who has won 59 doubles titles, and partner Chan Yung-jan will face India's Sania Mirza and Belgian Kirsten Flipkens in the third round of the women's doubles tournament.