Aging/Dev. speed decide the amount of value.
This is an example.
With default setting(1.000) of dev speed; Player A has been developed his power from 20 to 50 during 3 years.
With double setting(2.000) of dev speed; He would be able to develop his power from 20 to 80 during 3 years.(When he has enough potential) / or 20 to 50 during 1.5 years.
The value means speed. 1.000 means 1x speed while 1.500 means 1.5x speed.
also target age means when players start/end his developing/aging.
For example, With default setting, player may end his development at 25 and start his aging curve at 30.
if you set to target age both later, than he will end his development at 27 and start his aging curve at 32.
But remember, changing Target Age will not impact to amount of rating increase/decrease. It moves only 'Target'.
To summarize:
1. If Dev target age is set to earlier, than prospects will be able to debute in earlier age and reach their peak much ealier(not faster)
2. If Dev target age is set to later, than League's average debute time will be later.(not slower)
3. If Aging target age is set to earlier, than players will start their aging curve earlier. Also this means time of maintaining their peak after he reached is shorter.
4. If Aging target age is srt to later, than players will start their aging curve later. This means players will be remain at his peak much longer and they will be able to survive on MLB much longer but also prospects may has to wait more times.
sorry for ugly draws but you can see graphs what I said about.