After taking amlodipine for 20 years, how long does it take to get out of system?

Amlodipine has a long half life so it hangs around for a while. Here are the details:

Amlodipine has an elimination half life of 30 to 50 hours.
This is the time it takes for the drug levels in your plasma to reduce by half.
For a drug to be totally eliminated from your system it takes around 5.5 times the half life.
As an estimate then, after taking a single dose of Amlodipine it should be out of your system after 11 days. (5.5 x 50 hours = 275 hours or 11.5 days)

However other factors to consider include:
1. How much and how often you have taken the drug.
2. Your metabolic rate – a slower metabolism will increase the time a drug remains in your system.
3. Your age and health – older age and poor health will generally increase the time the drug stays in your system.
4. Body mass – generally the bigger you are the longer a drug will remain in your system.

https://www.drugs.com/pro/amlodipine.html