If I was to tell you to keep all your levels at 1 and then get 99 Strength, could you do it? Probably would take you a couple of years....
Training is definitely a challenge if you do not know really the only way to train you Obby Maul pure to these levels. The spot you will train in is called Relleka. If you take a look at your world map, it is rather large village, located north-west of Seers Village.
To get there, go to the Grand Exchange (GE) in Varrock and buy teleport tabs. You will want teleport tabs for anywhere you need to go as a pure. For right now, you should get Camelot Teleports. Simply type in the city you need and it will say "Camelot Teleport" so click on it. Buy as many as you can afford, or think you need. I would recommend buying in bulk as you will want to train without having to run back to the GE to get more.