This seems to be a regular for me now, coming on here and getting advice from actual gamers is better than google now. Anyway.
Just been informed that i am able to get a mount at level 20 for my blood elf mage, where do i obtain training for Apprentice riding?

I believe you can learn the Apprentice Riding in any major city. However, you'll only be able to purchase the level 20 mounts from your respective race vendor (blood elves in this case). The blood elf city is Silvermoon City. You can find the trainer and mount vendor southeast of the south entrance to Silvermoon City. This link will show you a map of the location:

http://www.wowhead.com/npc=16280

I think you'll need roughly 3-5 gold to purchase the riding and the mount. If you've got the money, it's definitely worth buying.