I encourage you to read research literature from the last century. Given that all of our linguistic estimates put Proto-Indo-European itself at around 3000 BCE, it makes no sense to claim that the RigVeda was composed earlier at that time. Indeed, Sanskrit likely did not exist at that time.
I can't trust the linguistic estimates fully as they are vague and are prone to many assumptions and approximations in their calculations. Just like change of stance of Max Muller, such estimations change depending on whether much older antiquities have been excavated or not. Like RigVeda described Saraswati during its time as alive.( I was mistaken that river dried in 5000bc, it dried around 3000bc to 2000bc ). It's only a matter of time since new evidence are discovered that pushes such estimates further back in time.
What they do very well imply that certain developments happened a 'minimum' of years ago.
Authorship's mention of time as in rig veda cannot be completely discarded out of consideration.