How can a young person stay on the path of purity?

Psalm 119:9-16

9 How can a young person stay on the path of purity?
    By living according to your word.
10 I seek you with all my heart;
    do not let me stray from your commands.
11 I have hidden your word in my heart
    that I might not sin against you.
12 Praise be to you, Lord;
    teach me your decrees.
13 With my lips I recount
    all the laws that come from your mouth.
14 I rejoice in following your statutes
    as one rejoices in great riches.
15 I meditate on your precepts
    and consider your ways.
16 I delight in your decrees;
    I will not neglect your word.