would a 2004 jp freeride 145l be a good beinners board?

Do you pick things up fast? Have you windsurfed before at all ever? How big are you?

If you've had a few sessions on proper beginner boards then you should be able to make the transition.

It'll be a touch harder to learn on than a true beginners board, but it'll probably do and will last you longer than a true beginners board.

Would definitely put a nose protector on it to prevent giving it a crack with the mast.

Should be a really good board to learn on as long as you have had 3 or 4 sessions on a bigger board already. Once you have the basic principals figured out on the 180L + board you will progress pretty well on a 140litre providing you are not a real heavy weight. 1 season on a 145 litre Freeride and you be ready to move on to something smaller still.
I went from 180 l+ for 3 lessons, then bought first board,a 140 litre Funride which did me for the next 8 months on which I learnt all the basics. I weigh 67kgs.