Both my nephews seem to have speech issues. The 8 year old has major trouble with Rs and is often not understandable. The 3 year old has problems in general so much so that my 3 and 4 year olds don't want to play with him because they can't understand him (we are working with our kids, don't worry about that). I have spoken to my sister about it and she is basically in denial. She sometimes makes the 8 year old repeat himself, but even then he doesn't really have the skills to fix the word properly.
When is too young to diagnose and help with a speech impediment and when is it too late to truly fix the problem?