It does not happen all at once. Boiling frog, eta 5 years. The warning signs are pain after a coding session, maybe a 2 or 3 on a scale of ten. However, eventually it gets worse. And your youth will act as such that the pain goes away. After a long weekend, you are recharged and re-healthy. That is a falsehood. Eventually, it gets to the point where the pain never goes away, it just subsides, constant background soreness, maybe on a 2 to 3 on a scale of ten.
Don't take your typing ability for granted. RSI can be managed but never completely cured.
The same traits that may make us good problem solvers (focus - as in not getting up, breaking that slippery, seductive state called "Flow", OCD - ignoring some things to focus, sometimes right, sometimes wrong on certain aspects, sedentary habits (biking FTW)) can make RSI an eventuality for a few.