Parthasarthi,
Set Planning Horizon at MRP group level and assign same MRP group to your material master and re try it should work because Maintaining a planning horizon helps the system to plan only those demands, which fall in the planning horizon starting from today. When an MRP Run is taken, the planning horizon is number of work days as mentioned (let’s say 180 days) from today’s date; the system would not plan any orders whose start date lies beyond this horizon.
BR
KK