As far as your expectations as to how long it might take you to get back your game and what level you can get your game to after a 20 year layoff would be based on two main factors.
Firstly, how good you played before you stopped playing 20 years ago, and secondly, what age are you now? If you quit at 20 and you are now 40, you’ll realistically have more time to get your game back than say if you quit playing at 50 and you are now 70.