The terms and conditions of sites like YouTube and Facebook require a reading age of at least 18 to be properly understood, the BBC has found.
The minimum age to use apps is 13.
Firms could be breaching European data rules, which require them to clearly spell out how they use personal data.
But many tech sites say they are working on improving the legibility of their legal documents by introducing easy-to-read summaries.
Read the full story, and learn about how tech companies use your data, here.