Jumping a horse...what age??

I wanna start training my horse to jump when he is 4.
But today my trainer told me he is actually 4. Because he's in his 4th year as of january 1st. But he dosent turn 4 till june. Its confusing. But shud I start now then? Or when he actually turns four?

And any guidelines to how much to jump at what age? If I jump once a week??

You could jump him very lightly if you want to. For about 10-15 minutes over small xrails. I would wait until he is truly 4 to start harder jump work though

Keep an eye on this thread. The girl seems to have the same dilema as you do
What age to jump my horse???? - Horse Forums (HGS)