Think about it from the actors perspective, not yours.

Do you think a 40 year old man would mind spending the time traveling
to and from your location place and doing an audition without knowing
that you are only looking for women three in their 20's, a teen boy and
a 60 year old grandfather type?

Now look at it from your perspective. Do you want to spend time auditioning
people for your movie that you know you don't have a part for? Is that a
good use of your audition time?

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The aim of an argument or discussion should not be victory, but progress.
Joseph Joubert, essayist (1754-1824)

Couldn't agree more with CI. Actors always prefer to know exactly what kind of part they're auditioning for.

Now, if your script has four best buddies, and they're all same (or similar) age, you can obviously consider same candidates for different parts. Your actors can still be initially called for a specific part, but you'll have a chance of offering them something else if you find a better fit for each part/actor.

all u need to do is make a list of characters that u want in ur film. Then advertise tht u need someone to play blah blah blah in ur movie. u will probably have less to worry abt this way.

Sabrina