One of the first things my physiology tutor asked of us was who has A level biology next thing he said was well forget it, it's what you learn from now that counts.
it's not unusual for 'A'level textbooks to have several missing words/typos in them. Inserting the word 'typically' would improve the sentence. You could write to the publishers suggesting that so they consider it for the next edition.
Yes, but 'early in life' doesn't just mean children, it includes young adults as well, in which case 'typically' would be correct.
However, I agree it could be open to misinterpretation and I would certainly give a fuller explanation if writing to the publishers which would include the information that over 40% of diagnoses occur in adults over the age of 30. https://www.sciencedaily.com/releases/2017/11/171130214925.htm
I would write to the exam board rather than just the publishers, copied to the school. The school can tell you which examination board they use.
Send some links about research and to this: https://www.diabetes.co.uk/diabetes-types.html
and tell them that they must take the correct information into account in any examination questions - otherwise you/any parent can formally complain.