As a grown adult, there is no fixing it. There are just ways to work around it that I've learned at my older age. But I am not surprised he has never talked about it because it is not something I ever bring up with my oldest. I speak in front of large crowds a lot as well, but in a smaller setting, you will definitely notice it. Don't be afraid to ask him, but people handle it differently when asked about it. Obviously if any if my children ever ask, I would never get offended or make them feel like they did something wrong, but anyone else that ever has asked me, I get kind of uneasy even talking about it.