IEMs are a big investment, so I can understand if you have hesitations about committing to customs, if in a few years she grows out of them.
I see this as a two part question. Let me break it down.
First, let’s look at impressions.
In terms of minimum age to have impressions taken. It depends on who is taking the impression, either an audiologist or hearing aid dispenser. Audiologists can do very young children sometimes as young as 6 months old. Hearing aid dispensers can’t do children under 13 years. However, this may vary from state to state.
As for how young to get IEMs. I wanted to turn this over to our Audiologist Ann Mundell-Noel, M.A., F-AAA http://www.ultimatehearing.net/
There really is no “minimum age”, as the monitors will protect the ears from loud noises at any age. The cost to “remake” in-ear monitors is minimal in comparison to the security of protecting hearing for a lifetime. If a child is regularly exposed to loud sounds, protection should be used regularly. Ultimate Ears is the answer!
Yes, ears grow, yet it is not predictable on the number of years they will fit. As an example of a custom product- I purchased custom orthotics for my son, age 13. The podiatrist told me they’d last 3-4 years…my son grew so fast, they didn’t last a year! So much for predictions…he is now 6’ 7"- hardly average If the child is regularly performing, he/she is a candidate for in ear monitors!