Yes, a 19-year-old girl can date a 20-year-old guy. The one-year age difference is relatively small, and in many places, it's completely legal and socially acceptable for individuals of these ages to date. Age differences in relationships are quite common and are generally considered a personal preference.
However, it's essential to consider the legal age of consent in your jurisdiction, as laws regarding the age of consent can vary from one place to another. It's crucial to ensure that any romantic relationship is consensual and lawful.
Additionally, apart from the legal aspect, factors like emotional maturity, common interests, and compatibility are important considerations for any relationship. As long as both individuals are comfortable with the age difference and have mutual respect for each other, there is no issue with a 19-year-old girl dating a 20-year-old guy.