I had recently asked a question on growth charts and the chart which i refer shows growth till 18. is it true as i have been growing in the 50th percentile from when i was about 12?

Basics: Linear growth (height) continues until the growth centers in the bones close. This varies with age/gender based on genetics/nutrition & hormone activity. Most who stay at the 50% for years will continue there until they stop.The only way to truly see if you can expect more growth is to x-ray your wrist/hand & verify growth centers are open to new growth.