Why am I getting pimples im a 20 yo?

No one is immune. While teenagers are more prone to getting "pimples" or acne due to hormonal changes affecting the environment of the skin, it is still possible and common for older people to get this - if keeping the skin clean and over the counter remedies (and time) don't resolve the problem then a primary care doctor or dermatologist can offer other remedies that may help ie. Antibiotics etc.