Regardless of its ECL, a monster with class levels uses the base attack bonus and base save bonus progressions of its class (rather than the progression shown on Table 1-1_ until it has 2- character levels. Begining with its 21st character level, it uses the progressions shown on Table 1-1.
In any other place in this book where "charater level" is indicated, you can use effective character level instead. For example, a creature with a level adjustment of +5 who is also a 13th level fighter/3rd level blackguard is ECL 21 and eligible to select an epic feat provided he meets the prerequisites.