The old one i.e, the milk tooth is over-retained.. which is required to be extracted so that it gives space for permanent tooth to settle the arch , if at all I is hampering in eruption of the permanent one

6 years is the exact age when the first permanent teeth which are the first molars erupt in the oral cavity. The upper front teeth can erupt simultaneously or slightly ahead of this eruption schedule. They are erupting on the back side because there is no proper space for them to erupt because the predecessor has not been shed till now. The width of the permanent teeth is wider than the deciduous teeth and the jaw growth compensates for this discrepancy. This is absolutely normal and the symptoms, if any, are to be taken care of by simple remedies.  Make sure tooth brushing is not compromised because plaque retention can be the reason for increased inflammation and discomfort in the patient. Regards.