Yes, teens can take part in the nightly Kariokie. When I went on the elation this past september, they had it in a lounge called the col porter lounge... That was a family room and it was alot of fun. I dont know if its called the same thing but teens can deffinatley do it too.
The first hour is generally for any age. After the first hour, any age can still sit in there but only adults can sing.
Each ship has their own rules regarding this.
Some say after 10pm - 16 years and older...some say "adult"....some say 18 years and older.
Just depends on the Karaoke Host.
But all ships offer at least one hour each night for those who are not "adults".
Also, Circle C and Club 02 (depending on their age) also has karaoke offered several times during the cruise. That will be listed in their Capers.