Is it okay to let the basil leaves "age"? Like the leaves at the lower part of the stem. I pinch back my basil plant at the top, so the leaves at the bottom doesn't get touched and grow larger. I have read in a forum that the big leaves don't taste as good as the new small ones.
The larger leaves don't necessarily have poor flavor. It's more about age than size. Old leaves don't taste as good as new ones. That's why a good harvesting system is key.
Most people try to do this by harvesting the oldest (lowest) leaves as the plant grows, before they get too old. While this can work, it's not the most awesome method for plant form and longevity. A better harvesting system not only harvests a good crop, but also prunes the plant for best form and productivity. Here's how it's done (taken partially from this article, which is spot on):
When your basil plant has 3 to 5 sets of leaves, cut the top off just above the second set of leaves from the ground. The single stalk will now end here, and two new branches will now bud and grow from the set of leaves you left behind.
Every couple of weeks, repeat the process, cutting just above the first or second set of leaves on your newest branches.
If the plant flowers, it will set seed and die. If you see flower buds, you can try to keep up with cutting them all off as they form (beleive me, it's more challenging than it sounds), or you can let it go and start over.
You use these young new prunings s your harvest, with awesome rewards. and it will be quality, young basil. From here:
Harvesting basil this way, you'll probably be able to get 20 cups of basil from each plant per season!