I now have little over 21,000 miles on my S2000. And I noticed that the brake feel softer than before. Is it time to change the brake pad?

 

Check 'em first. That's how you determine if they need changing. You take a visual measurement of how much is left. I don't know the exact measurement but I'd say if you're getting down to 1/8" or less of material on any given pad, it's time. If your pedal feel is getting soft, your car may be in need of new brake fluid and a bleed even if the pads are OK.