Vito, Clemenza and Tessio were contemporaries, and were about the same age. The actors who played Tessio and Clemenza in their youth in GFII were chosen, in part, because they bore some general resemblance to Abe Vigoda and Richard Castellano in GF.

The scene that you cited is one of the most important in the entire GF Trilogy because it shows Vito, who previously was almost shy and retiring, deciding to take his fate in his hands and start on a life of crime by killing Fanucci. It also shows an important transition among the three pals: By being the only one who has the coglioni to stand up to Fanucci, Vito asserts himself as the boss of the trio, instead of Clemenza. Note that, previously, Clemenza was acting like a bigshot, and bossing Vito around. If you own the DVD set, you will find a couple of deleted scenes on the extras disc that are very revealing: After the dress robbery, Clemenza makes Vito wait in the truck while he has sex with one of the women he's selling dresses to, then orders Vito to make more deliveries. But in another deleted scene, after Vito kills Fanucci, Clemenza is very humble (doffing his hat in Vito's presence) as he introduces the young Hyman Roth.