Teaching horse to canter on lunge

I recently bought a new horse; about 14 years old. Before I had him the woman didn't ride him a lot, and only at a walk. Before that he was left in field with cows for probably about 8 years.

When I ask him to canter under saddle he understands that he needs to speed up, but he doesn't get that he needs to change his pace. When I ask him to canter on the lunge he doesn't get it at all.

I have searched all over google, asked my horse friends, I can't find anything! Any help would be great.

Thank you!