My boy had nippers used on him when he was 10 months old. His first trim was at 5 months and I believe the first time nippers was used was when he was around 8 months. It depends on how long the foot is and how much needs to be taken off. I could trim his feet using just a rasp if I wanted to, but nipping off most of the overgrowth then rasping them clean is a lot easier on my rasp and my back lol.
If you think there's a trimming issue, you can post some pictures of his feet to get an opinion from a few of us.
And your farrier is wrong about his feet not being an issue right now. In fact, right now is the most critical time for his feet to be correct. It sets a foundation for his future soundness and can impact how he grows and matures. It's best to be proactive to ensure he's growing correctly, including the feet he walks on.
ETA: Change all those he's to she's lol. I'd love to see pictures of your little filly!
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