With my son, it didn't happen until age 8. Looking back, it had always been around (always meaning from age 2 or 3) when he stopped singing/humming... And started chewing on his lips (bruising them, so we NONE of us (my family is chockablock with med pros) including his actual doctor, caught it.
It wasn't until he got a Nasty chest cold at 8. Nasty like pneumonia, bilateral pleural effusions, etc . Nasty that. that triggered uncontrollable bronchiospasms. PRIOR to that, he'd just run run run (adrenaline opens his airways AND causes them to shut down. It's quirky.). We spent Feb-June in and out of Children's Hospital. (Not the whole time. The longest stretch was 5 weeks, shortest was 1 week.)
So the meds saved his life.
He's VERY responsive to meds IF he gets them fast. If not, then it takes weeks to stabilize him off supplemental oxygen. (Most asthma kids take a day, tops, when things get bad... So no worries. My kid is quirky. Medically "interesting" :P He just starts going into respiratory failure.
But until 2 years ago when he got that cold... The only obvious side effects were blue lips and no more singing. (He sings all the time again, now!) we didn't SEE the blue lips until the first time on O2. I'd actually been snapping at him again to STOP biting his lips. O2 mask on = pink lips in seconds. Not. Bruising. After. All.
There was collective head meet drywall by surgeons, nurses, and research scientists on both sides of my family when that happened. It's why docs don't treat their own kids. Too. Close. To. See. And kiddo had -just bad luck- never gone blue during a doctors appt. so they missed it. His lips WERE bruised. They got numb when his 02 was low... So he'd chew. After adding 4L of oxygen, though, the bruises were in a pink background. Ugh.
2years ago and I'm STILL beating myself up over this.
He's on controller meds (that make him fat and give him insomnia), and uses his rescue inhaler 3-4 times a day.
So in addition to saving his life, its also changed our lifestyle a lot.