What does mean if i have narrowing of disk space in l4-s1 level?

Maybe nothing : Your spine looks on MRI like 30% of asymptomatic 30 years olds many narrow disc cause no pain at all 95% of backache ismuscularand resolves overtime and can be controlled w ith commonsense avoiding activities.

You are older than : It means you are older than 10 as degenerative changes can be seen as early as 10. Years old and continue as you age. The lowest 2 levels of the spine are the most involved, typically. This is the l4-5 and l5-s1 levels. These are age related changes that are significantly accelerated if you smoke and/or obese.