Yes, my very first maremma was a 7 yr old spade female.
I searched high and low for an experienced dog because I was moving much further out, it was December, lambs were due to start dropping in Jan, and we had NO fencing on a virgin farm in a heavy predation area.
I was panicked... whew... it was a long few months til spring... we had cattle in cattle panels, sheep in electro netting with barn access, and used a stall of the barn for the chickens that winter and kept them totally confined.
I finally found an experienced maremma I could afford... took the gamble (she was still pricey)... best money I ever spent.
I had her brought down from upstate New York the first week of January.
I was skeptical how she would do at 7 yrs of age in a new environment, new owners... we put her with the sheep that night in the barn on a cable... she settled right in.
We kept her cabled for a few days since all we had was electro netting... after the third day, she was turned loose inside all the netting with the sheep... she's been here ever since until I lost her last Monday due to complications from surgery :-( She would never leave her livestock for anything. The lambs slept with her... there is still a picture of her on my web page - I haven't been able to take it down.
I now have another 7 yr old who I didn't raise... a male I got when he was 6 months old (he is 2 now)... and one I raised who is 18 months old.
So... I have a few youngsters but really need another... I have no "old" dogs right now.
The seven yr old female is (or will be) bred to my male... I hope...
(Unless she has a huge litter all pups are spoken for - thought I'd toss that in).
In "my" ideal situation, I'd have a pup coming on about every 3-4 yrs. I like to work them in pairs whenever possible - especially out on big acreage. They rest better when they do sleep and work great as a team... amazingly well actually. They each establish their own "job" and "role" on the farm and all work together, even if they aren't in the same pasture. For my purposes, having at least 3-4 is necessary.
A word of caution to anyone considering lgd's.... the one disadvantage is that they do bark. More than 50% of their job is "to deter". Barking at threats is the way they do that. If you like in the city... it's a very rare ldg (of any breed) that wouldn't be viewed as a nuisance if they are really doing their job correctly.
They do not nuisance bark (or shouldn't anyway), but they do bark when they think there is a threat. It is their JOB to do this, so they should NEVER be fussed at for it. That's hard to do when they are right next to the house at 3am and have a opossum cornered who they are just certain is going the eat all their sheep.
So... holding yourself back from fussing at one who lives in the city would be quite a challenge.
As another side note: A lot of people ask me why I chose maremma instead of pyrs. I don't want to knock the pyrs, but many of them have had the instinct bred out of them. But, the biggest reason is because maremma work totally different... they stay "with" the livestock as opposed to working the perimeter of the property. I wanted protection where the livestock was.