People keep saying that but the evidence is there that it's a 25-to-29-year-old man's game right now.
Yeah, times have changed quickly and talented teens and guys in their early 20s need to persevere down in the lower regions of the game much longer than before, and so those at the top of the game are much older than before, but still.. 25-29 year olds are still young men. Sports like Tennis are designed for people in their youthful physical peak. There aren't many occupations where you gotta start thinking about moving onto your next stage in life at around 30, because you're now too old for your current job.
As we are now, I'd agree it makes sense to call those 25 and below, young guns.