DMG p.231
A character who agrees to training as a reward must spend downtime with the trainer. In exchange, the character is guaranteed to receive a special benefit.Possible training benefits include the following:
The character gains inspiration daily at dawn for 1d4 + 6 days.
The character gains proficiency in a skill.
The character gains a feat.
Does this means that if I find someone willing to train me I can gain a feat at any level?
For example, I am a rogue and help some animals in a forest that a retired ranger protects. In gratitude for what I did, the retired ranger told me that he is willing to teach me the Dual Wielder feat. So I can learn that feat without the need of being a 4th, 8th, 12th, 16th, or 19th level?