at what age do you start to feed betta fry regular food?

Answer 1

kinda depends on how fast they have grown, but in general at about 1/2 they can handle some finely crushed flake food as part of their diet. Swap over slowly to get the used to the new food and to allow smaller one's to grow a bit more. Not to say you need to swap them at a young age that is. The longer you have them on live foods the better for the fish IMO.

Answer 2

By "regular food" I assume you mean betta pellets. I usually waited until the fish were full grown since the pellets tend to be too big for most juvvie bettas' mouths. (They do sell pellets for baby bettas but sometimes they are hard to find.) It's always hard to transition them from live food to "dead" food though so if they are still kind of young but not quite full grown, and still are in that "I'll eat anything" mode, it's easier to get them to eat pellets.