PDAs are cute
I'm so soppy about stuff like that...occasionally I have actually stopped and said "aww!" at cute couples in the street.

Old people shouldn't do it :S <<< that's mean i couldn't do it

Perfectly fine as long as its respectful. Stopping in front of someone sitting on a bench to kiss is not respectful, etc, being right in someones face, or continuously. I don't see why people walk, stop, and have a nice tonsil licking. It doesn't make sense, I can understand standing there having a romantic moment, its sweet, but just randomly stopping etc is like, wtf etc. Holding hands, cuddles and kisses are fine. No matter who it is. -kissing for the wrinkleys tho. XD Though people who sit there sharing little kisses every 30 seconds or who are like MWAH MWAH MWAH MWAH MWAH like some old auntie are like DDDD:

Are okay only when I'm not single anymore

Ok for everyone, as long as old people don't do it

If it's a constant 'omg I've gotta be attached to this person at all moments', ie alot like what `guruubii said, that's a no.

However if it's just holding hands and the occasional quick kiss, I don't see the problem with it.

Old people like me shouldn't do it

On either side of the argument, the ones doing or the ones watching. I say to both: GROW THE HELL UP!

totally fine, just no unnecessary groping

Should not be.
if your hormones are so out of control that you cant keep your hands of someone in public aor have respect for other people, you need medication or therapy

There is nothing more annoying than being scrushed by hormonal perverts on the bus, or trying to complete a transaction on the till listening to the nauseating sound of their faces sucking on each others lunches.

Grow up, get a room, and keep the action in it.

my 2 cents :>