Yes your uncle may apply for CAT exam when he above 30 year old. There is no age limit in CAT exam for MBA.

There is no such age factor taken into consideration for giving CAT exam. They need to have 50% of passing marks in degree/graduation.
For SC/ST than you need to have 45% in degree/graduation

Reservation:

15.00% Scheduled Caste (SC)
7.50% Scheduled Tribe (ST)
27.00% Other Backward Classes (OBC) candidates belonging to the “non-creamy” layer
3.00% Differently Abled (DA)

MBA degree has more value and companies will not be optimistic, whether a student is completing MBA at whatever age. Depending upon the requirement company will be hiring you.

The Common Admission Test is an all-India test conducted by the Indian Institutes of Management (IIMs).

CAT is as an entrance exam for admission to the Post-graduate and Fellow Programs in management courses of several management institutes all over India including the IIMs.


Test Duration & Pattern:

Section No. of Questions Duration
Quantitative Ability 34 3 hrs
Verbal Ability & Reading Comprehension 34
Data Interpretation & Logical Reasoning 32
Total 100