My DD7 is phenomenally fast with picking up cello. She started only 18 months ago, but is already very fluent. She's working towards ABRSM grade 4 at the moment. I attribute her rapidity in learning cello to her focus: she is intensely focused and will literally choose to play cello for hours on end. She loves it to bits, which is so thrilling. Her VCI is 155, so perhaps that has helped.