Of course! I'm a self proclaimed Delve simp lol
You can start right away, but only tiers 1 - 3. Then at 80 you unlock the higher tiers up to 11 by completing the tier right before it in any delve. But the drops don't get better past tier 8, 9 - 11 are just for acheevs and unlocking the "secret delve", which has two tiers in itself "?" and "??"
That's the beautiful thing about delves, it's end game content for folks like you and I. Take your time, gear up as you can. There are seasons for it, but if you don't get through it you're not missing out on anything but cosmetics. Even the great vault gives delves (and world content) love!
I have unlocked all of the customization I wanted for my Delve mount in Warcraft! I'm a happy moose!
I think the last time I had this much fun in WoW was... I think Wrath? I loved Wrath so much. Probably my favorite expansion up until now. But with the story getting back on track (imo), and Devles? My god I'm in heaven. This expansion is a solid 8/10 so far.
Thank goodness for long updates otherwise this place would be a mess!