The only thing I would watch now, that I used to, is Only fools and horses. It never gets old.
I wouldn't watch anything old now. I have tried (e.g. on Youtube; Thundercats, The Mysterious Cities of Gold, Neighbours, Home and Away) and they just seem naff now. It was sort of nice in some scenes that brought back the feeling of being 8 or 9, but it only lasted a second.
Saying that, my partner has just watched the entire (old) series of Dallas