I'm very much a "move fast" kinda guy. The philosophy being that if it looks and feels good, invest in it - physically, emotionally. Stop being afraid of getting hurt. You can't win the lottery if you don't buy a ticket. You can dip your toe in the water for six months and not know what it's going to feel like when you're immersed. Jump in ... if it feels good, stay in, if it doesn't jump out. You'll have saved six months of your life.
You'll never learn about each other by "dating," when everyone is on their best behavior. Learn about the DLSs (dirty little secrets), foibles, peccadillos and you'll get the full picture. My ex-wife and her daughters had a saying that they "smelled his breath." What they meant was that when you're in the first flush of love you ignore the little negatives, like bad breath, but one day when you wake up and it pushes you away, you know the reality ...

Feckin hell...I can't tell when someone is flirting with me so that whole "moving to fast" thing has a snowball's chance of happening for me. Then again, my life is more than half over, is there such a thing as too fast?

You can " " when you are typing too fast because words are missing.

It's not a bad thing at all - as long as your partner is moving at a similar pace.

But if not ... well ...either adjustments need to be made, or "boom !"

Another thought: what do you consider ‘too fast’? Is it one partner, or both? I think we each have our own comfort level.
Mine is, taking enough time to know that other person very well. See them angry, frustrated, sick. Have a few fights. Find out if the communication is good. Can they give a real apology? Respect my boundaries? Can we compromise when there’s conflict? All that takes time.

Not for me. As long as I'm protecting myself (and not being stupid), I don't regret getting caught up in the romance of a possible new love.

It is for me. I attract narcissists/toxic people, and one of their hallmarks is lovebombing, sweeping a victim off their feet, mirroring their every desire, and moving very fast: faster than most are comfortable with, to control and hook in the victim.
That being said, I had a set of in-laws who married only 6 weeks after meeting and were devoted to each other for 55 years. Died three days apart. So it does happen in healthy relationships.

That just never happens for me. Moving too fast is a red flag, and I always put on the brakes. If the person is reasonable and agrees to slow down without going psycho...excellent sign. If they go nuts: bullet dodged.