CountIF with two conditions

Hi, i've read other topics about countif with two conditions, but didin't had a satisfatory answer for my problem.

I have a sheet with two colums:

A B
NAME AGE


A B
ROGER 18
ANDREAS 42
CARL 21
MIKE 05

This sheet has over 10.000 lines ^^.

I'd like to count how many of these people has age between 0 and 5 years (math transcription >=0<=5), 6 and 10 (>=6<=10) and keep going...

I've read about sumproduct, many topics change countif to sumproduct, but it doesn't help me at all...

I created another column with the variables writen in math formulas, for ex:

Column D
Line 1) >=18<=24
Line 2) >=25<=30
Line 3) >=31<=35

and then i tried to link this cells as a condition of the countif formula. for ex.: =COUNTIF(A4:B4;D2), but it doens't show me the correct result, it always shows "1".

If someone could help, 'l appreciate it.