I think - like in most conflicts the truth is somewhere between the parties.

OTOH you want to look young. In my mind this is always a question of taste. Your look is not his taste. But your look is YOUR taste. He should not hurt you with this, it is always possible to talk about things with normal words.

OTOH perhaps he is a little bit (!) right with claiming your look being the look of youngsters. See, perhaps he does not want that people are aiming their forefingers at you. It seems like he does not want a g/f in his arms that is looking like a child. Do you understand the other point of view a bit?

So my idea for you of what to do is:
Try to understand the point of view of your partner, you of him, he of you. Check out if you want to move towards each other. Listen. Think. Be patient.

Best wishes GeSt

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If every material thing is gone, my smile and my tears stay left.