Most BJJ schools are pretty stringent with belts, especially as they get higher up the ladder. It's a direct reflection on an instructor and if they hand out BJJ belts like candy, their school can get a bad reputation really fast via word-of-mouth.
And don't get discouraged by being worked over by a much older purple belt, it's just a good sign that he's got good skills and training at the school.
If he keeps catching you with the same sub, sweep, position, etc.....be sure to ask him for a point or two on how to address/avoid. Most upper belts freely dispense advice and appreciate being viewed as a training partner, friend, etc. rather than an opponent.
Of if you have an questions here as well.....I'm injured (running injury, not BJJ) and not able to roll at the moment. And I know better than to even get on the mats to coach b/c I'll end up rolling despite my Dr.'s warning.
Consistency: It's only a virtue if you're not a screw-up.