Asked for female, 27 years old from Hyderabad
It's difficult to assess when you say lean. Let me know his actual weight.
Again weight is not an indicator of health. Plump children are not necessarily healthy. As long as your baby is eating healthy and has reasonable weight, there's no need to worry.
Regarding his teeth, you can easily wait till one to one year 3 months. Some get tooth later. All babies are unique. So don't compare with others.