We have a horse at my barn who only has one eye! He is an event horse and is one of the most trustworthy horses we have.
I would think twice. If you really really like him and you're like, this is THE horse!, then take him. But if you want a jumper, you have a beight long future with, i would definately go for a younger horse. A cloud in the eye isn't a "healthy" sign. A cloudy eye should be checked by a vet. Before you buy him really do ask the current owner if they have ever checked the eye and if they have, what the Diagnosis was.
There are a lot of good horses out there. Good luck:)
If you liked and work well with him do it. Age shouldn't be a factor unless he's already slowing down. The cloud in the eye as long as it doesn't bug him don't worry about it. (I have a one eyed jumper so they can do well without it) but I always suggest talking to a vet, doing a PPE, and talking to your trainer and such about future goals for you and if the horse works
Age doesn't matter soundness matters! If you like him/enjoy him, get him if not don't. It would be a great learning opportunity.