Recently, I've heard or read that question, and I confess that I am getting more than a bit pissed off by it.
'Oldhammer' is a very recent term, but it's not 'official' or 'sanctioned', nor is it sacrosanct and above critique.
People who were in many cases not even there at the start of the Warhammer craze, or whom were just wanks waiting to get lucky (as we all were at some stage) have somehow become arbiters of taste and propriety in the fields of vintage gaming, and it just isn't right and proper.
OK, I would say that if you were there between 82 and say 89 you witnessed Warhammer at it's pinnacle ,before it became that over-hyped cash cow we all know today. If you played the game in the first two editions and especially the first, then you'll know that in those days, you didn't need 'official' models, that there were more companies making wonderfully strange and beautiful figures which could be dragged into the game (more on this anon) without you being castigated by your peers. These were not the days of the red-shirted fanboy, paying for his room in his parent's basement with a weekend job at his local GW store. No sir, the staff in those days were imaginative, independently minded. They were bastards of the old cut, who would tear you a new asshole, if you didn't stop acting like one.
I have seen home cast models, lined up with Citadel, Essex and Ral Partha, all doing a sterling job as Undead, facing off against 15mm historical models, doubling as Gnomes. Those involved were playing rather than arguing over what was and what wasn't 'proper'.
Frankly, it mattered not one fucking jot, what was on the table, so long as you knew what everything was supposed to be for that game.
You really had to have been there to get the vibe. If you are asking 'Is this Oldhammer' you are really asking 'Is this contemporary to the 'classic' pre 1989 era?'.
Look, if the models give you a buzz, don't all look like parodies of the creature they are supposed to represent, don't require a special set of sub-rules to use them and most important of all in my book, give you a real sense of pleasure to play with, then you are in the 'Oldhammer Zone'.
If all you can do is follow a 'company line' and not take responsibility for the evolution of your own fantasy world; or, if you can only read something if it's stamped 'official' then you may as well go and take up another hobby because you don't really get what Warhammer was all about. It's called fantasy for a reason - It's imaginary. It does not need rationalisation beyond 'It just does'. You can have all the 'fluff' in the world, but unless part of you and indeed your gaming buddies is invested into the gaming sessions, then it's like eating processed food against freshly prepared.
THAT is Oldhammer! It's a mindset, a sense of style, and feel. It's also one which every 'old sweat' has their own take on. None of them are right or wrong - just different.
Now, go and find those plastic tortoises that you got from the Xmas crackers, stick some old Runequest Newtlings on their backs, give them a 3" move and 4.5" charge with a 5&6 saving throw and play a bloody game. If someone tells you that your stuff is not Oldhammer, poke them smartly in the eye and ask them politely to fuck off and leave you alone, or join you for a game.
Most importantly, have fun...
PS: Don't get me started on people who look down on those who play fantasy and despise historical gamers or vice versa...