I am looking at Wawrinka's career stats on wikipedia and I am impressed with the fact that his win/loss percentage in slams is just over 10% higher than his overall win/loss percentage. This all thanks to his career blossoming starting in 2013, at Australia, where he was a couple months shy of his 28th birthday. It's even more impressive than Agassi, because Agassi prior to his comeback in 1999 was already a mega-star of the sport. He'd been a contender at slams since 1988 and while he went away after winning Olympic gold in Atlanta in 1996, he was a guy that everyone saw as a danger man in slams, as he had already won a few, been world #1, and actually was seen as a major underachiever. He missed opportunities in the early 90's and had 'tanked' matches even earlier in his career. Made the semis in two slams as an 18 year old in 1988, another semi in 1989, two finals in 1990, one final in 1991 and finally won his first 22 in Wimbledon in 1992. Not to bore everyone to death with stats, but just pointing out that Agassi's 'second' career 1999-2003 (period where he won slams) was impressive, but this is what most expected him to do a decade earlier. Wawrinka was nowhere near the semis of slams in his teens, he made it into the top 10 when he was 23 and the top 5 years later.
Angelique Kerber is a good comparison with Wawrinka. She made it into the top 10 around the same age Wawrinka did, and won her first two slams in her late 20's (last year). It'll be interesting to see what she'll do in the coming slams. Will she sneak away another title like Wawrinka? Wawrinka still has to play Nadal on Sunday, and you never know, if Stanimal is indeed in Stanimal mode, then he could win his 4th slam. 4 finals, 4 titles. I am not sure If Kerber will match that. I am also not sure if any of the current players that in their mid 20's, soon to be in late 20's, and lurking 5-15 rank, can do what Wawrinka's been doing the last 3 or 4 years. I am talking about guys like Nishikori, Raonic, Dimitrov...Cilic I can't really put in that category because he already has a slam, and in my humble opinion, he is capable of getting more. Del Potro is the exact same age as Cilic, and he got a slam early in his career, but unfortunately injuries have prevented him from truly blossoming. I am not sure what he'll be able to bring later in his career.