Could I please have some advice and suggestions?  My two cats were
best of buddies for about 10 years, when the male died.  I replaced
him right away with a 2-year-old male from the shelter.  Tried to pick
a "laid back" one, but it looks like I guessed wrong.  Sully, it turns
out, is a very playful, very vocal, very energetic shorthaired tabby,
almost kitten-like in his behavior sometimes.  The old female (aged
about 12), accepts him, and seems to want to be around him, but when
he is feeling rambunctious, which is often, he will play-pounce on her
or play-bat at her, ususally resulting in her yowling and hissing,
then running away to hide.  I've given him "time outs" in his room
when he does this and admonish him in a deep voice.  I've gotten some
control through this to the point where if I deepen my voice when he
gets ready to pounce, he will sometimes stop and crouch low, as if he
knows he is doing something that he will get punished for.  But it
still goes on.  They've been together now for about two months.
Bringing him back to the shelter does not feel like an option.  So, do
I:

1. Keep intervening, trying to reward positive behavior and give time
outs for bad.
2. Just let them alone to work things out.
3. Try to make the most of a less-than-ideal situation until the older
cat eventually dies; then get another cat who's personality matches
Sully's more closely
4. Get an additional cat right now
5. ????

Sully is calm sometimes, and the two sometimes hang out in the same
room in a relaxing way; they eat together without incident; Sully
likes to lick/groom the older cat as well, which she responds to with
purring.  My feeling is that--when the unpleasant instances happen--he
is also frustrated because he wants to rough-&-tumble play, and she
won't play with him.  She is still eating and grooming, but she is
forced to manage her life in the house now around a companion
who--maliciously or not--sometimes harrasses her.
 Sorry for the length of this.  Any thoughts or advice would be
appreciated!
Joe