Is Botox safe for forehead lines in my mid-20s and how many units are usually needed?

Hi doctors, I’m thinking about getting Botox for the first time to reduce mild forehead lines and prevent deeper wrinkles in the future. I’m in my mid-20s and my lines are visible mostly when I raise my eyebrows, but they are not very deep yet. I would like to know if Botox is a good option at this stage for prevention. How many units are typically recommended for the forehead area for someone my age? Also, will the results still look natural if a small amount is used? Thank you for your advice.