please tell me which one is correct.
My younger brother is taller than me.
My younger brother is taller than I.
My younger brother is taller than I am.
'...than I' is correct grammar, but in colloquial speech, sounds too formal, and so most people would use the form, 'than me."
'..than I am' is correct grammar, and sounds a lot less formal than "..than I.' Another example of its use would be:
He: Mary looks about 40.
She: She can't be! I'm 41 and she's a lot older than I am!