Peanuts are an oddity in the veggie world. They continuously set new flower and new peanuts as long as the vines are alive. You can actually dig out the peanuts at the crown of the plant and so long as you don't disturb the roots too much, they will continue producing more nuts from the new flowers.

The key to harvesting them is to find the point at which the maximum of mature nuts are under the vines. The best way to tell is to pull up one or two plants and if you see a nut or two at the crown starting to sprout, then they are ready or nearly so. Don't pull the biggest plant in the patch, get some that are just average. The biggest plants are going to be more mature than the average.

DarJones

thanks fusion

I checked my plants, there were some nuts that had were either sprouting or didn't look good, but the majority were underdeveloped.
I found somewhere mentioning a hull-scrape method to check if the peanuts are ready. It involves checking the color of the peanuts shell after you scrape some of the outer layer away.
Can't really tell where one plant ends and the next begins, but pulled up ~2 plants and decided that they are not quite ready yet. On the plus side I was able to plant a sprout into the space the pulled up plant vacated. I'll check the plants again after this set of rainstorms.

I would suggest cracking a few of the peanuts. If the nuts are firm and fully developed and the shells are thin and hard, then they are mature. As above, it is a matter of determining when the maximum of mature nuts are under the plants.

From your description, you planted them too thick. This seriously delays maturity and harvest. Peanuts should not be planted closer than 6 inches apart in the row and rows should be at least 30 inches apart for most varieties. I plant mine at 8 inches apart in the row because that is the optimum distance for the variety I grow. I have another variety that has to be spaced 12 inches apart because they are much more vigorous and sprawling.

DarJones

Peanuts mature between 90 to 120 days depending upon variety.Virginia Jumbo peanuts take 120 days to mature where as Spanish peanuts take 90 days to mature.I take these as guiding times.For long summer seasons it is good to wait till leaves dry out to brown or yellowish brown.In any case there will be few unripe nuts even the plant has reached maturity time.
Here in Maryland I must dig out the plants before frost some time in October.We harvest the hard solid looking nuts and let go the tender white looking ones.We usually boil the nuts adding salt and oregano and freeze them to use year round.