The younger the tree the more responsive to pruning generally. I grow a lot of trident and Japanese maples here and let most get to more than 1m tall, often to 2 m tall before chopping back to somewhere around 15-30cm. Usually trunk chop in conjunction with hard root pruning in winter. If the roots are cut bleeding is not an issue for maples so that can be done any time from mid winter through to bud burst in early spring.
Tim S picked up that your tree is a lace leaf variety. Do you know the variety name? Is it grafted? The weeping dissectum type JM have a reputation for being less hardy than many of the upright varieties so you may have to proceed with more caution than I have recommended above if that's what you have.
I was more asking about pruning because of the way this tree has grown. I was worried that the leader off to the side had become too dominant and that if I let it continue that way it would be more dangerous to the health of the tree to remove it later on.
From here i think that stronger trunk will be your best bet for the main trunk of any bonsai. The smaller one is far too straight for my liking but if you are happy with straight and vertical go for it.
The bend where the stronger one is growing would make a nice first bend in any future trunk (remove the smaller one completely at some stage). After the initial trunk chop and regrow further chops will give the trunk bends Adams technique aims for. The initial grow period can be longer to get the trunk thicker. Successive grow periods get shorter and shorter as the tree nears completion.
Although it sound simple, getting a good result may be more challenging and require a few attempts to get the sequence and timing correct + not every individual maple will always respond as planned so you do need to allow for some less than ideal responses.