Motor skills certainly improve as you grow up, and hand-eye coordination improves, too. I don't know that reaction times do, I wouldn't think so because that is simply the wiring of your brain. But it has been shown via MRI that the brain really does change its wiring until early 20's, which is why you have the odd and erratic behavior of youth until you have finished 'growing up'. So maybe there is an optimum wiring, that improves reaction times to maybe peak in your mid 20's, too. Then it is downhill from there as you continue to lose brain cells for the rest of your life!
Neuronally, yes, motor skills improve with age. However, with age comes other physiological problems...perhaps a reduction in connectivity between these "motor neurons". The reaction time may decrease with age as the myelin sheath wears down on nerves and neurons...which reduces the conductivity, and slows the speed at which a signal it can be sent.
You're right, MRI has definitely demonstrated brain plasticity (changes) in early 20s. You might be surprised to hear that this actually continues until the day you die. It's just that some of the most profound changes occur from birth to about 20. But as people age, their situations change, their daily environment changes...all of which affect the brain's "wiring". And yes, as you age and lose neurons, they're gone forever. So, as the old saying goes, "use it or lose it!" There's many 50 or 60 year olds with brains similar to 20 year olds....thanks to daily use (e.g, crosswords, puzzles, reading/writing, math....just make yourself think).
This is fun!
