If the weight is correct...

My 200g girl is eating one rat pup twice a week, and I think she'll be ready for weaned next month. As someone said, go by the largest part of his body.

As for feeding mice or rats, that is your choice, but rats are usually more economical in the long term (one rat vs. 3+ mice when your snake is bigger). Some people will tell you that rats are more nutritious. Personally I can't get live rats so mine have to take f/t rats or mice.

Feeding f/t or live is also a personal choice, there is plenty of info on this forum and elsewhere to help you make an informed decision.