A Problem with the French Language (for English Speakers)

In French there is a verb “tutoyer” this means to use the familiar form of you. Many languages  have different forms of you, German, I am told, has nine different forms of you but English just has one you (in the past there were thees and thous), today the same you is employed for addressing a child, for addressing a president or for addressing several people. The same word you can be subject or object. I am thus not sure when I can address a French “friend” as “tu” instead of “vous“so I ask:

Me: Est ce qu’on peut se tutoyer?

(Can we use the familiar form of you? i.e. tu/toi)

French “friend”: Oui, si vous voulez.

(Yes, if you wish. But uses the polite form vous to me so I’m still unsure whether I should proceed with addressing him/her as “tu” or “vous“).

Sacré Bleu!