My DD is 19 months old old.
On days I work she usually does:
In the A.M., Lunch time, When I get home, after dinner (once or twice) then bed time, so a total of 4-5 during the day and 2-3 times during the night.
On days I'm home she nurses much more frequently...Probably about 6-8 times during the day and a few at night
She is usually in charge of letting me know when she wants to nurse. i haven't limited times or anything like that. *Occasionally* I will try and distract her if she's nursing very frequently and I think she's just bored. If she really wants to nurse she won't be distracted. Usually when we are out of the house, she nurses less.