13 year old eats with his fingers

There are some cultures where eating food with ones fingers is considered the norm. As Robert124 has said, it shouldn't be a problem if your son's hands and nails are clean.

Although I would never attempt to consume something like soup without the use of appropriate cutlery, I am not averse to eating food with my fingers. Sometimes I find that the weight of cutlery is too heavy and I just haven't got the energy to hold it, or use a knife and fork to cut food into smaller portions.

During the colder months of the year, I find that metal cutlery can sometimes feel so cold that it's like holding blocks of ice. If I'm eating food that requires cutlery, then I will sometimes wear a pair of winter gloves.

Conversely, I dislike eating with my fingers, I prefer to use cutlery as I don't want to touch it.

I love the feel of well balanced knives forks and spoons. They should balance on your middle finger. 

It is sensory but the other way around.

I guess we're all different :-)

I wouldn't eat fish and chips with my fingers.

It's not entirely consistent though as you can't eat an orange any other way, or sandwiches.

Conversely, I dislike eating with my fingers, I prefer to use cutlery as I don't want to touch it.

I love the feel of well balanced knives forks and spoons. They should balance on your middle finger. 

It is sensory but the other way around.

I guess we're all different :-)

I wouldn't eat fish and chips with my fingers.

It's not entirely consistent though as you can't eat an orange any other way, or sandwiches.