I have a lot of qadha roze and I'm not sure how to fulfil them as I have heard that if we intentionally leave a fast then we have to fast for 60 days continues? I didn't start praying and fasting just as I turned 9 but I started doing it really late so how am I supposed to fulfil about 4-5 years of qadha fasts + the fasts that were left because of mensuration?
I actually never knew that we were supposed to fast when we get to 9 years of age and my parents never really said anything towards it. But now that I'm older and have started fasting all the days of ramadan except for the days of mensuration, im wondering how do I do it?

Then (because you were ignorant of the rule), you just need to make up the missed days only, and feed a poor person per day for delaying the making up (Qadha). That is 750 gms of flour or rice (22.5 kg's for a month), which could be given to a poor person (Food, not money).
If you missed 4 months of Ramadhan, then you need to fast 120 days (not necessarily continuous), and give 90 kg's of food to poor people.