To tell tha age

[svetik]

Could you please say if all these sentences are correct. Thank you
1.He is 4 years old
2.He is a boy of 4 years old.
3. He is a boy of 4 years.
4.He is a 4 year old boy.

 

[Kondorosi]

Could you please say if all these sentences are correct. Thank you
1.He is 4 years old
2.He is a boy of 4 years old.
3. He is a boy of 4 years.
4.He is a 4 year old boy.

1, 4

 

[rlfwood]

Could you please say if all these sentences are correct. Thank you
1.He is 4 years old
2.He is a boy of 4 years old.
3. He is a boy of 4 years.
4.He is a 4 year old boy.

#1 and #4 are correct current usage.

#3 is an archaic usage that you might find in older novels, etc.

#2 is not correct.

 

[svetik]

Can we also say?
1.He is a boy of 4
2.He is 4

 

[rlfwood]

Can we also say?
1.He is a boy of 4
2.He is 4

Yes.

 

[Barb_D]

I would add that you should use hyphens: a 4-year-old boy.