Its nothing to worry about condition as per erupting tooth he is 6-7 years of age so, its just the 1st molar is coming up into the oral cavity, so minute gums is left ,when it will fully comeup into the cavity there will be no gum structure left over that portion which is rightnow your concern.
Next Steps
just make him brush twice a day especially in that area
Health Tips
dont let anything stuck in that area, if ever get stuck anything let him brush, or sqish or rinse with normal water