First of all, congratulations! For your first grow, that's an excellent result, brother 😃
It seems to me that they are at the right height, more than 70% of the pistils are dark, however, there's a more efficient way to check the harvest readiness, through the color of the trichomes. They start translucent, then turn a milky tone, and finally become amber. When they are 70% amber, 29% milky, and 1% translucent, you can harvest.
I recommend leaving them in complete darkness for 48 hours before the harvest; it will stress the plant and make it produce more compounds, including THCA. Don't forget, a slow dry, around 11 days, good air circulation but never direct air on the buds.
I hope I helped in some way 👊👽