The reason for not mentioning older animes must be, that most people cut down on their top 5 by the question "What anime would be the best from my present point of view?". To say that you enjoyed those older animes a couple of years ago, so they must be very good is as wrong as to always name the newest animes because you`d like to watch them right now.
In the first case you didn`t know the newer animes back then, so if you just remember how much you liked the old ones in the past you don`t give the new ones a fair chance. In the other case, if you`d have to decide what anime you would like to watch right know, you`d probably chose an anime currently running.
Also, I asume that your taste changed over the time. If I think of myself when I first watched anime, I enjoyed stuff very much back then, that I would rate "OK" at the most by now. Again, to rate the old animes after your "old taste" and use your new preferences on the new ones would give new anime a disadvantage.
If you think those old ones are still great, then there is no problem naming them here though.
enough talking, here`s my personal top 5 (no order, it was hard enough to cut down on 5):
- Witch Hunter Robin (for the plot, the mood and Robins cute hairstyle
)
- Scrapped Princess (for...I just love it ...
)
- 3x3 - Eyes (for cool evil demons, even cooler magical powers and a lot of mystery )
- Jin Roh (for me this is the best [and saddest] anime movie ever )
- Azumanga Daioh! (for the fun part in my top 5
this anime showed me the true meaning of "rofl" )