You should not add anything to your tank while it is cycling, fish or otherwise. You need to cycle your tank with raw shrimp or something similar. It is cruel in my opinion to cycle a tank with anything which is alive.
That being said, here is the scoop on anemones. First, they require pristine water conditions, as in undetectable levels of ammonia, nitrite, nitrate, perfect and unfluctating PH and salinity, temperature, alkalinity, the works. Lighting must be metal halide. I have yet to meet someone who could keep an anemone for any significant amount of time on anything but MH lighting.
Now this is a personal opinion and is based on my ten years of reefkeeping; age of a tank is not really that relevant. You need to age your tank to make sure it is stable, but that is about all. You could have a tank which is two years old and still not be able to keep anemones. You need to have a stable tank with proper parameters and lighting. You also need to protect your intakes so that they do not get sucked up and die, releasing gastric juices into your water and killing everything in there.
Don't just take something because it's free, could have some dire consequences. Good luck though, but I would take that anemone in for some store credit. Also, be aware that anemones move and can sting corals as they do so. I have a 125G reef and it will never have an anemone for this very reason.