My first daughter was turned the first time at 11 months old, almost 20 lbs.
I didn't know any better at the time, and I thought that almost being 1 and 20 lbs was good enough.
Then, a year later I bought the Radian because I knew I wanted her harnessed as long as possible but it was cheaper than a Britax. I found this board when looking for reviews on the Radian (after I'd already bought it).
I learned about ERF and turned her back around at 24 months and about 24 lbs.
I turned her around for good just a month before she turned 3.
I did it then because of her age, I didn't want to RF past 3 (unless I had a way tiny kid). She was 28 lbs at the time. Oh, and yeah she was in a Radian 65.
My youngest daughter I just turned around to FF about a week or 2 ago because she is close to 32 lbs now and her seat (a Fisher Price Safe Voyage Deluxe) only goes to 33 lbs. She is 26 months old.
I had to arrange my carseats to fit 3 across for my new baby due in a few weeks, so I had to put my Radian in the center to do that. I have my youngest in the Radian now, and my oldest in the Fisher Price Safe Voyage Deluxe. I hear it's better to have the least protected in the center if thats possible, and since they are both FF, the least protected is the youngest one.
My new baby I hope to RF to age 3, but if I can get to at least age 2 (by weight, I don't know how big he will be or how fast he will grow) then thats fine with me too.