In school at age 10 (IIRC, many years ago), we were using Bunsen burners, heating stuff in test tubes, melting and drawing glass rods and tubes etc. However the class size was small, the supervision was close, the teacher had many years of formal teaching experience, and, back then it was a far less litigatious society.
With eye protection, and appropriate clothing (no synthetic fibre outerwear, long sleeves & trousers) the risk of serious injury is low, but you cannot reduce the risk of a burn requiring hospital treatment to zero.
IANAL, but would think it reasonable to require a written acceptance of the risk assessment from parents of children under 16, and if they themselves don't solder, they should be taught beforehand so they can give informed consent.
What the cut-off age should be is a very difficult question. Some children shouldn't be allowed to handle hot, or sharp objects, poisons or power tools until they are full adults, and even then should be discouraged! Others are fine at a much younger age. Maybe consult a local junior school science teacher to find out what age they start working with concentrated heat sources and high temperatures?
As its an introductory/basics class, IMHO it would be entirely reasonable to require 1:1 supervision from a parent who has already taken the course or demonstrated competency, to allow under 16s to attend.