The approach is going to depend on what you define as un-touched, how much time you have & your skill set. The horses age is not relevant.
With a wild horse or one I canít walk up to and catch I would put them in a round pen & work them from a saddle horse with the intent of eventually roping them. After I have a loop on them I can get them comfortable with the rope on their body, then teach them to release from pressure of the rope with some time. As the horse progresses I work toward getting my hands on them and building some trust, then I can get a halter on. How fast I progress through this would depend on the individual horse. This can also be done from the ground, but itís just easier from a saddle horse and the presents of a calm saddle horse can sometimes comfort the un-touched horse youíre working with.
If the horse is not wild but just leery of human contact or If youíre not handy with a rope I would just do enough ground work to get him following me in the round pen. With consistent ground work you will eventually be able to catch the horse and put a halter on. Once the halter or rope is around their neck its just a mater of teaching the horse to come off of pressure.
I left out the details, but in a nutshell that how I do it.
Best of luck