If so, how?l can flex him laterally, but l wanna keep him limber at the poll too and l can not get on him yet.Any tips?Is it possible?
(l can ride him, but we do not have an indoor arena and the ground is too hard right now to ride)

l am not sure but due to some research, on the horse u can do this.
You get ur horse responsive to the pressure first at a stand still. Ask ur horse to give to the bit, he will probably step back, push into the bit, sling his head. Just hold ur pressure constant, until he ever so subtly tilts his nose in.

Once he does that, immediately release all pressure. Ask again & repeat.

Once he is solid at that, move to a walk. l hold pressure & drive the horse into the bit (all done in a snaffle, no leverage bits), they horse will bring their nose in but l hold my pressure where l had it in case they tip their nose out again.

So basically the horse will ride on a loose rein, flexed at the poll, but if they do tip their nose out, there is a pressure reminder if they run into my hands.

Yes you can.

Is this horse bitted yet or still to halter?

You can do it either way.

If halter, attach leads to each side and just ask for the horse to go vertical in the face for you, the horse will probably back up and just keep with them, but eventually the horse will tuck its chin, INSTANTLY drop all pressure on the ropes and reward heavily.

Keep working it until he is softer and quicker.

You r more than half way to ur goal. Lateral flexion is the key to vertical flexion. l really would not worry about the vertical until u ride. If ur horse is soft in his face & flexes laterally to the girth line, he will be easy to encourage to vertical flexion if he has the confirmation for it. Just make sure that u reward his slightest effort so he understands he did the right thing. l would definitely do the flexion exercises in a rope halter instead of a bit, but that is just my choice. l never want to have a surprise that would give a young horse a bad experience with metal in his mouth. You have plenty of time, do not rush.