Should i brush my teeth after lunch?

If possible, yes: At your age, you should brush your teeth twice daily. After breakfast in the morning, and before you go to bed at night will generally provide you with the cleaning you need. You don't need to brush your teeth after lunch, and most people don't, but if you have the opportunity and want to, go ahead. If you don't, however, you should be fine.

Yes: Yes, it's best to brush and floss after each meal. Before you go to sleep would be the most important time not to skip, followed by after breakfast. It only takes two minutes to do a thorough job and well worth the time and effort over the long haul. Try to at least rinse your mouth out thoroughly when you don't brush and floss.

Depends: If your meal was highly acidic it's best to wait an hour before brushing. You need to brush at least 2x/day (3 is better) for 2 full minutes by the clock. I think it's better to brush before breakfast to remove all the harmful plaque that can turn your breakfast into acids. After meals if you can't brush at least swish with water and swallow. Additionally using floss/water pik/or other adjunct.