Why doesn't Lady Capulet want her husband to get involved in the fight in Act I, Scene I?

In Act I, Scene 1 of Shakespeare's Romeo and Juliet a brawl breaks out in the streets of Verona between the Capulets and Montagues. The fight is initially instigated by the servants of Capulet and further provoked by Capulet's cousin Tybalt. Hearing the disturbance in the street, Lord Capulet emerges in his gown and calls for his "long sword," presumably to engage the Montagues in a fight. Lady Capulet is right behind him and remarks,

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In Act I, Scene 1 of Shakespeare's Romeo and Juliet a brawl breaks out in the streets of Verona between the Capulets and Montagues. The fight is initially instigated by the servants of Capulet and further provoked by Capulet's cousin Tybalt. Hearing the disturbance in the street, Lord Capulet emerges in his gown and calls for his "long sword," presumably to engage the Montagues in a fight. Lady Capulet is right behind him and remarks,

A crutch, a crutch! Why call you for a sword?

She is suggesting her husband is too old for sword play. Capulet is not to be dissuaded and counters that Montague "flourishes" his blade in defiance. Lady Montague offers basically the same suggestion to her husband. She says, 

Thou shalt not stir one foot to seek a foe.

Immediately after the Prince breaks up the fight and declares that the death penalty will be enforced if any more fighting occurs. Of course, this edict foreshadows the fight in Act III. 

The idea that both Lord Capulet and Lord Montague are too old to fight is reinforced in the next scene while Capulet talks to Count Paris. Capulet says,

But Montague is bound as well as I,
In penalty alike, and ’tis not hard, I think,
For men so old as we to keep the peace.