you're 25, your body will hide it's weakness much better than your later life.
The danger of bone density loss can and most likely will occur. It's going to be even worse for you to judge the bodies slow deterioration due to low bmi because as a runner you must be used to a higher pain threshold and push through any niggles....until the damage is irreversible.
instead of picking a random CR percentage / calories, first get your BMI to healthy normal range ... 18.5 then whatever calories your body needs to be at that BMI, stick to them, this way you are getting the best of both worlds, your doing everything science says that will help with longevity and optimal bodily functions.
I would say go for 19.5 BMI then stay on that for a year and once your bodies adapted, slowly over years reduce your calories and see if you can maintain a BMI of 19.5, if not then that is your target.
every bodies are different. Matt (another CR member) was consuming 1600 calories and able to maintain a BMI of 19.5, he also went really low on his BMI and did as I outlined, increased his BMI to 18.5 and reduced his calories later while his body still kept the extra weight.
If your goal is longevity with a body that is able to withstand your lifestyle then honestly you are in dangerous levels, you are risking a future where you start having bone density loss and would lose your ability to exercise, to do normal activities!
Is betting (since it's still not guaranteed CR actual works in humans) on fragility and disability (very likely outcomes if you keep your BMI at 17.8) on an "potential" 5 years (if your lucky) of extra life?
as Dean mentioned this must be such a shock and takes some time to accept but do it slowly, take a month or two to get to the healthy BMI. Honestly think rationally and think smart. Sometimes we try to bite to much and end up sick from it when we could have gone nice and steady. Keep us update and good luck on this "recovery".