Playing a string instrument IS a highly intricate skill, requiring a lot of time, patience and consistency. I believe that regardless of age, a student has to put at the minimum half an hour a day of practicing time. Understand that that half an hour will cover the basic skills needed to maneuver around the instrument. The half an hour guideline is BARE minimum! Most of my students are NOT future professional musicians, and yet – that is what I ask of them. Kids ages 4-9 should still put in half an hour a day, possibly splitting it up in three ten-minute sessions: one before breakfast, one right after school, and one before or after dinner. The consistency is imperative, even in short sessions, very similar to dog training! ( you  are more than welcome to meet Schubert, my well-trained, and yet nutty chocolate labrador retriever!) Again – every day, even it is a short session is better than missing three, four days and then doing one day of practicing for two hours.