I think this question depends on your age and where you were living many years ago. If you lived up north and were clubbing as early as 87' you might say that oldskool is just 87'-93', but if like myself you lived south and only realy got into things from 91'-97' you might say oldskool is between those times as thats how i remember things.
Personaly as a south lad it was all fast breaks and mad jump around the room stuff, so Hardcore, Happycore, Hard House, Rave and Gabba are oldskool in my book. I personaly don't like Hip-Hop, Rap, House or Garage stuff really at all and had never classed it as 'oldskool' just as 'old' untill i found this forum lol.
Everyone i know where i live would say the same as me on this, but take that idea north and you would get the oppisit responce, so the fact is 'oldskool' depends on what clubs you went to and what style of music you 1st heard back in those days when you were having a great time and gettin' wrecked.
We love the tunez we do coz they remind us of past times and great feelings, so at the end of the day 'oldskool' is diff' for everyone. You can't put a small block of past years on the word and say "That's oldskool!" at the end of the day if a tune is 10 years old, it will be oldskool to someone no matter what style of music it is imo.