I really don't know. Maybe because she's talented, pretty, a good trash talker.
Get it, trash talker! Because she used to be a junk yard dog!

No, Buster is nowhere near Angel or Scamp's age. Remember, Tramp and Buster were friends at one point, so Buster is an adult. Other than that it's just a cartoon, so I guess Buster just had a crush on her.

all i know is that Alissa milano the creater from angel said that: angel is a pup,, buster is big but sometimes he acts like a pup sow maeiby thats why he likes angel,, but still idont like that couple,, angel and scamp are a better beatyfull couple,, they deserve to be with eachother youst look at them toghter there sow cute toghether,, even ife u dont like it,, they will still be toghether beacuse the creaters made them to be thoghether and they will always will be... plus ife they make a 3 movie u will know the truth even ife u dont belive it

Buster is a genuine flirt. Plus, Doberman's are big dogs, he may be closer to Angel's age than you think. And with mates, I don't think--with dogs in this case of animals--that age really matters in anything. Although, yes, you're right, it is pretty weird.