Don Ottavio’s age is a crucial part of how his character behaves, the consideration of his effectiveness is at the core of his actions. From a historical perspective, it would be natural for Ottavio to be an older man in relation to Donna Anna- in fact, he could very well be close to the Commendatore’s age, or slightly younger.
This choice, as mentioned before, makes sense from a historical perspective (it is hard to conceive that Donna Anna would have had much of a say in the choice of her fiancé at this point in history and social rank) but also puts a contrast between Don Ottavio and the titular Don Giovanni. Giovanni is young, strong and full of energy, whereas Ottavio is no longer the young man he used to be: his actions are covered with the extra layer of caution one is likely to acquire with age (if not through more judicious thinking, then at least out of self-preservation.) He is far from being Don Giovanni’s physical equal and to confront him without solid evidence (which he gets at the end of Act I) is to take unnecessary risks.
Age also changes the perspective from which he attacks his two arias. “Dalla Sua Pace” sung by an older Ottavio must acquire a certain melancholy: he wishes for nothing in the world except for Donna Anna to be happy, and his happiness is directly tied to hers. He is an older man who now must be more than a future husband to his distraught fiancée, he must adopt a paternal position (Don Ottavio as an older man is reinforced in Act I, Scene III, No.2 where Ottavio says “lascia, cara, la rimembranza amara: hai sposo e padre in me” during their duet immediately after discovering the Commendatore’s body) and his first thought is not one of avenging Donna Anna, but a gesture of affection and a mature reflection on their intertwined fate.
“Il Mio Tesoro”, on the other hand, becomes the moment of redemption for Ottavio. In the face of all the atrocities committed by Giovanni (and which link him to the original crime- the Commendatore’s death) he can no longer be cautious or hesitant- it is time for him to finally awaken and bring much-delayed justice to bear upon Don Giovanni’s head ( with perhaps the best moment for a full dramatic awakening of the character happening on the “vado” of “a vendicar io vado!” which culminates on a held high F, and which descends down an octave.) This is the moment in which Ottavio passes from reasonable doubt to absolute certainty, and it should reflect in the character’s expressions and movement, his sense of resolve has shifted from protecting and comforting Donna Anna towards full retaliation. In truth, Ottavio’s turning was triggered at the Don’s party, but this is the first time Ottavio has an opportunity to have a moment all to himself, dramatically.
Ottavio’s heroic purpose is not insincere, but fortunately he is spared having to deal with the Don himself: his purpose and morals are noble, but we have already seen the Don is most capable in a fight, and we get the impression Ottavio wouldn’t survive a duel with Giovani. Rather, the Don finds death comes to visit him as a result of his own actions--- leaving Donna Elvira to find closure, Donna Anna to mourn, and Don Ottavio to hope perchance to marry her someday.
If Don Ottavio is played as a young man, I think it would be important to play him as a younger man to Don Giovanni: whereas the older Don Ottavio is at a physical disadvantage to Giovanni, the younger Ottavio would be at a social disadvantage. As a younger man Giovanni’s ‘friendship’ to him would become more of an older man(mentor) to a young man recently introduced to society (and perhaps even add an extra layer of deceit and cruelty to Giovanni’s actions, since he essentially might have befriended Ottavio in order to get to Anna.) Having Giovanni be Ottavio’s mentor figure would explain Ottavio’s reticence to act from a different angle—Ottavio has grown accustomed to Giovanni’s front as an honorable man, and is loath to think that someone who has been such an important figure to him could be two-faced. Also, being older than Ottavio, Don Giovanni is more established a name in their society of nobility than the younger man, thus making the prospect of accusing someone with greater influence a daunting one.
In both cases Ottavio is cautious and needs proof before he acts, but in each case it comes from a different perspective (or end of the age spectrum, as it is.)
The other issue at hand is that of social rank: Giovanni and Ottavio are both equals in rank, though we don’t know exactly how powerful each truly is (who has a greater number of land, riches, etc.) The nature of their stratified society makes dealing with Giovanni a more difficult matter, since although nobles could adjudicate to lower classes, targeting someone in the strata of nobility was tricky. Frank E. Smitha writes that “In Spain the landed aristocracy was holding on to its powers, and many if not most Spaniards clung to the values of the aristocracy. They believed that business was fit only for Jews, Arabs and other foreigners. (…) Spain's nobility was one tenth of its population. They spent some of their fortune seeking government office, and in government, it is said, were thirty parasites for every man who did an honest day's work. Some of the nobility maintained customs barriers as a source of revenue, taxing commerce and driving up prices.”
It is clear that Giovanni has been getting away with his trademark conduct for some time, and that he has not come to an untimely death only to the possibility of his influence. No amount of influence, however, can eventually keep his misdeeds from coming to a head—Don Giovanni as an opera demonstrates what is possibly the worst day in the life of the Don, but also the breaking point of the privilege which has shielded him for so long—he has accumulated outrage after outrage and strung them up through his life like a collar of pearls. The end of the opera shows what happens when the string breaks and the pent-up hatred he has accumulated runs unchecked: his enemies gradually hound him to destruction. The true catalyst (in the opera) of Don Giovanni’s misfortune is Donna Elvira, whose mixture of insane devotion and righteous revulsion allows Ottavio and Elvira to find an ally, and sets the Don’s doom in motion starting at the end of Act I, with the Don’s apparent victory (by escape.)
Ottavio at his very core is a noble character. He is not ideally heroic, as his caution robs him of the opportunity to end evil before it can cause more harm, but he nevertheless does not waver when he knows that his course is true. To portray him in weakness is to mistake the nature of his character: he is not a dashing personality, his most natural impulse is to protect, and it is this impulse that he eventually must overcome in order to champion Donna Anna.
