What's the meaning?

These are posts users made on a thread with a poll for voting your age:

user1: I don't think I've ever seen a person over 60 operate a computer. Is that possible?

user2: Heh, I've even got a smart phone and have ppl to text with! Plus I installed the 2+2 app which turned out to be a pos that you shouldn't bother w/ if you have Opera-mini. (he voted 61)

user3: UNPOSSIBLE!!!

user4: old man shoes dropping knowledge (what does he meant here?)

Thanks a million!