True friendship knows no real age ! It matters not. Follow your heart.
Age does not determine the sincerity of a friendship.
Mainly true friendships and loyalties get to be tested in difficult times. When you need a hand who's gonna leave you and who's gonna stand by you.
As Rooster advised, follow your heart as i also would add, follow your instincts. Analyze, observe, test and give it time. Time is another key. Many underneath secrets show off with time.
The human behaviors itself can tell a lot about them. Study them and it can help you to understand more of the recognition between fake and real.
Friendship .. I mean TRUE friendship knows no boundaries in terms of age, size, race, family vs non family, religion, geography .. The list is endless. The only thing that may limit a friendship is trust.