Autoflowers showing pistils at just 18 days, anyone else had flowering start so soon? Anything to worry about?

Autos pushing preflowers is totally normal in it's third to fourth week. Even though your plants might feel too young to be hitting this stage, they'll continue to stretch over the next few weeks. It won't guarantee an early finish, though most of the autos I've grown where fast producers, I've seen ones that lean more sativa that flower for quite a long time.

Yes! I’ve had an auto flower in two weeks! And it didn’t finish any faster. It’s bad genetics. People don’t realize that autos are still not as stable as they can/or should be. Good luck! ✌️🏻💚🌿💨