Doubts & Questions

A couple of days ago one of my students, Alberto, posed an interesting question after warching a video about the new MacBook. Could it be said, "13mm thin", or "13 mm thick"? He argued that we normally say "the big" adjective, in examples such as "13 years old", "2 metres tall" or "3 hours long"

From my point of view, we use the adjective that interests us more, thus, 13 mm THIN, as we want to emphasize thinness. Were it be a mattress, it would be 100 mm THICK.

Here's another explanation:

"old" is an adjective, of course. 
"fifty years" is a noun phrase used as an adverb answering the question "how (old)?". 

How old is he? = adverb adjective verb pronoun. 

The pattern is NUMBER + UNIT + DIMENSION-ADJECTIVE 

Numbers: 3, 6, 10, 20, 75, ... 

Dimension adjective: old Corresponding Units: years, days, months, ... 
Dimension adjective: long Corresponding Units: miles, feet, yards, meters, light-years 
Dimension adjective: wide Corresponding Units: (same as for length) 

From this we get "How long?" "Five meters long." "How old?" "Fifty years old." "How deep?" "A millimeter deep." ... 

Exception: It's not "25 degrees hot", just "25 Degrees.

I hope it's clearer now!