Baghdatis was ranked #54 in the world at the beginning of 2006, nowhere near top 10. Also, tennis evolves over time, and I’d say it has evolved noticeably in 2023 compared to 2006. The new players are faster and stronger and the racket technology has become much more advanced.
Do you still think that it would be impossible for a very fit and athletic 18 year old guy from 2023?
Ok, what are you asking? Movement? Instinct? Forehand racquet head speed?
Since you name dropped 2006 Baggy, I naturally assumed you meant when he played the AO and made the final and made the Wimbledon semi. That would include his physical characteristics plus his general feel for the ball, plus his tennis IQ and experience.
If an 18 year old wants to be as fast in 4 years as Baghdatis was in that year, it is possible. If they want the same reaction speed, also possible. Racquet speed, also possible. In all purely physical characteristics it is possible even without necessarily having the right genetics for the job. Will it be easy? No. But with the proper training an 18 year old can get there reasonably quickly. But that would eat some time, getting to the proper physique for the job. Having both explosive speed and stamina to go at it for hours on end. Would take a good chunk of time.
Then there's the mental. Match Marcos' tactical knowledge in 5 years? Probably not, but maybe. Tennis instincts? No. Experience? Definitely not. Mental edge? Wouldn't count on it, even despite Baghdatis not being known for his strong mental game.
Even past general physique, I'll be generous and say each individual shot could probably be very well practiced (top college level) within 4 years of extremely dedicated work from a 4.0 (which isn't guaranteed at all). That still doesn't mean the player has a weapon, which is something more innate and based off of a preexisting talent. And putting those shots together like a pro? Not likely. The game is very different from the top of college compared to the pros.
Let's put it this way.
Going from 4.0 to 5.0 in a year is already ambitious, but let's say your 4.0 is a prodigy. He can do it in 6 months. The next 1.0 of rating is
much harder. No more fundamentals to get solid and just junkball. Real plays need to be made. So let's say they can do it in a single year (that's absolutely insane - like going from the worst player on a mid-level college team to among their best). Then they go from 6.0 to 7.0 in just 1 more year (nearly impossible - that's mid-tier college talent to the bottom of professional tennis in just 1 year). The higher you go, the harder it is to improve. Fewer obvious things, and the things you aren't doing right are already ingrained, so you need to unlearn then relearn.
Say he can do all this, then he's still 2.5 years into the training and he's at the level that dozens of players in America find themselves in every year. To go from the bottom of professional play to a grand slam semifinalist level in just 1.5 years is impossible. It's just impossible unless you're a prodigy who is a genius at the game and just needs to find the groove or grow into your body. Your 4.0 is neither. That final step is impossible, and it's already predicated on 3 almost impossible steps of their own in that time frame (4.0 -> 5.0 -> 6.0 -> 7.0).
It is unrealistic, otherwise more players would do it.
