Group and count by age breaks

For voyages (Years, ships), how can I group and count sailors by age intervalles in standard SQL?

YEAR    SHIP            SAILOR_AGE
2003    Flying dolphin  33
2003    Flying dolphin  33
2003    Flying dolphin  34
2001    Flying dolphin  23
2003    Flying dolphin  35
2001    Flying dolphin  38
2001    Flying dolphin  31
2003    Flying dolphin  36
2003    Columbine       41
2003    Columbine       42
2003    Flying dolphin  27
2003    Flying dolphin  51
2003    Flying dolphin  46

What I tried:

SELECT YEAR, SHIP, SAILOR_AGE,  COUNT (*) as `NUMBERS` 
FROM TABLE
GROUP BY YEARS, SHIP, SAILOR_AGE;

It give me the number of sailor for each year:

Example:

YEAR |SHIP           |SAILOR_AGE  | NUMBERS
------------------------------------------
2003 | Flying dolphin| 33         |   2

How Can group sailor ages by intervalles

Example:

From 20th to 40th year's old  
From 40th  to 60th year's old