Good for you for giving this some thought instead of fixating on an age and sticking to it. No one else has mentioned this, so I figured I would. A few years ago, I read that some big-name pediatric agency (like the AAP) was recommending a MINIMUM of 1 year of breastfeeding, and encouraged mothers to go to AT LEAST 2 years. Sorry, can't find the source, but it struck me at the time, since my daughter was just turning 1 and I had no intention of stopping at that time.
Also, consider that the definition of weaning is actually "to ripen", translated as "to be ready for the next stage". That means a true weaning is determined by the child, not the mother. Of course, nursing is a relationship, so a bit of nudging on Mom's part may be called for. Also, there aren't that many 2yo's who WANT to nurse more than 1-2x per day, so I think working together on weaning between the 1st and 2nd birthdays is great timing.
For myself, I decided I would nurse until my daughter lost interest, but I wanted more consistency in the time of day she could nurse. Also, if she wanted to nurse near a snacktime or mealtime, I offered food before breast. This quickly reduced our 6x per day to about 3x per day, where we stayed until she was about 20 months. Then she naturally fell down to 1x, and then stopped altogether. I'm embarrassed to say I have no idea what was her last day nursing (it wasn't long after her 2nd birthday), but I'm proud she weaned herself.
The Sears website has a good article on weaning:
http://askdrsears.com/html/2/t026400.asp
I wish you luck with this. Breastfeeding is one of the most rewarding experiences ever. It's great to end it well.
-K.