From Croydon, hop on Southern or Thameslink from East Croydon station

https://zionuuko161.theburnward.com/step-by-step-getting-from-victoria-to-gatwick-airport-by-train

From Croydon, hop on Southern or Thameslink from East Croydon station. Trains to Gatwick are frequent and fast, often taking less than 20 minutes platform to platform.