The website mentions the run will pass through Central Catchment, Mandai, Woodlands and Bukit Timah, so I think very likely it will be like the 2012 TNF SG 50km route which went as far as Lorong Asrama area (Energizer Night Trail venue).
You can still sign up for the run actually. From the FAQs:
Do I need to fill up the Indemnity form and seek parental/guardian consent if I’m below the age of 18 as of 25 Mar 2017?
Yes, participants below the age of 18 are required to seek parental/guardian consent before signing up for the race. They would be required to submit the signed Indemnity form during the Race Entry Pack Collection (REPC), failing which the Race Organiser reserves the right to refuse the entry of the participant. You can download the Indemnity form here.
But like what wonderfulblevic says, do take care of your legs and don't subject them to too much of abuse too early in your life, especially if you think you will continue to do this for a long time to come.