Funnily enough, I heard 'grand-frère' yesterday in an episode of the BBC4 French series 'Engrenages' ( Spiral)! , said by a fifteen year old about his 'big brother'.
Having said that I think it is regarded as childish, and you would probably say -
Mon frère aîné /plus agé
I personally have never heard 'vieux frère'.
Hope this helps!
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