" ‘I remember having sex with friends @ a young age; showers w/ my dad (probably not appropriate)’"I didn't ask how old she was when she wrote about it in her diary. I asked how old was she when they showered.
You are capable of understanding the difference, aren't you??
She was old enough to remember it, and to note that it probably wasn't appropriate (so she was probably old enough for it to make her uncomfortable). Plus, she writes it in conjunction to her having sex at a young age, so, unless you think she was having sex at 3 years old, it's likely her being a teen is accurate.