I had it for the first time at 46. Never had it as a child, despite repeated exposure, so I assumed I must have some sort of natural immunity (I had cowpox as a baby from my first smallpox vaccination, so had some reason for believing this). My son got chicken pox just before his 6th birthday, wanted cuddles for a couple of days, slight spottiness, and was fine within a week.
I went down with it 2 weeks later, on the plane returning home from the USA. Landed at 11am, attended son's speech day covered in spots (well, that's where it came from) and retired to bed for 2 weeks.
I was very poorly - the spots started on my face and neck, then spread downwards in waves. I was absolutely covered in them! They took a long time to fade as well - I still had marks on my feet after a year. I had spots inside my throat, which were excruciatingly painful; all I could eat was chipped ice and fruit juice for about 3 days.
It was the first time in my working life I had had more than a couple of days sick leave - and had to phone our personnel manager to find out what I needed in the way of doctors notes etc. Even the GP was impressed at just how spotty I was - I got my note!
So yes, in my experience, chicken pox in adulthood is not good news. So I am delighted ds got it good and young.
He has more scars than I do, though. We could not stop him scratching them...