What age do you consider " old enough"? If you think the average 14 year old doesn't now about hand jobs or blowjobs then you are deluded tbh!
Why would you rather young girls get misinformation from their friends rather than factually correct information from a book?
It's not a safe assumption. You just want to assume that everyone thinks like you!
There is a big difference between sex education and sex advice!
No 14yo needs to be reading about handjobs.