Tactician and being very thorough. I was also careful not to leave it running while I wasn't playing. I'm also currently 150+ hrs into elden ring and haven't beaten it yet.
I'm at nearly 300 solo hours so far. I'm working my way west through the lower city, and just got to the Blushing Mermaid. Is that around halfway through Act 3? It's my first run, so I don't know.
My completionist tendencies are in play here, so you might want to consider my hours close to an upper bound. (Unless you plan to explore both paths to the city.)
Playing with a group seems a bit like committing to watch a five-season TV series together. If you don't have time to binge, it might last for months, or even years.
We were pretty thorough with our playthrough, and even then missed things. Also I had to sit there for ages while my wife cosplayed as Winona Ryder and methodically searched every basket of rotten fruit for loot, just in case any of them had legendary weapons inside. They didn't, and we finished the game with enough camp resources for like 100 extra long rests.
Co-op was also bugged to fuck and we missed most of the NPC interaction. I strongly recommend a solo play as well.
You're likely about half way. I did a weekly co-op with some friends, about 3 hours per week, and it took from release (back in September) until just a few weeks ago (so, 6 months?).
Most of us have kids as well, hence the 6 month time-line. It's great solo as well, though.
I have a coop game with my wife too. We have about 40 hours on our clock too, and we just yet entered the Underdark.
At that pace I expect our game to last for years, because in my "normal" run I am at 170 hours and still have plenty to do.
You can of course do it faster, by lowering diffiCulty (we did) and by just following the main quest. But much fun lies in exploring the world and finding the many secrets.
My solo run took 100+ hours. Co-op runs tend to be slower. The game has three acts, as a rough estimate you can say each act is the same length. (This will vary wildly, act 2 can be very short and act 3 can be very long, act 1 can also be the longest as you're still learning the game.)
If you're not sure what act you're in, you're probably still in act 1.
If you can give details of what you're up to, I can tell you more definitely.
Co-op progresses at roughly time x players in my experience. Between people fucking up and requesting a reload and people taking bios/phone calls/requiring sleep.
I'de recommend playing it all the way through at least to the 3rd act as if at least one person has you'll have a rough idea how to progress.
Man, this is making me realize how awesome this game would be in a LAN setting.
Easiest way to tell is by level. If you're level 12, then you're ready to finish the game and won't be far of being able to do so. That's the best way to guess time left, spoiler free. I've completed a run in 30 something hours, and I've got one that is like 60+ hours long with ages to go.
As someone with two young children, I find playing with childless friends much faster as they can be flexible and play when i find free time than with childed friends on set weekly scheduled.