J.F.
Sorry if I repeat anything-I didn't have time to read the other responses. Both my son and daughter used a nuk. We got rid of theirs around 2 or 2 1/2. What we did was start little by little. We cut back to only naps and bedtime. Then down to bed time and then altogether. We didn't have any major problems with them really missing it doing it this way. They would inquire about it once in awhile, but then we would say they were all gone and it would be fine.
A couple other things I have heard of but not tried-my friends cut off the tips of the nuk and then told their child it was broken so they couldn't have it anymore. Don't know if at 13 months that would work real well...but it worked for them. I have also heard of telling them that other babies need them now and having them help you put it in an envelope and send them off somewhere.
I don't feel like it is a big deal to still have a nuk at 13 months, but it probably is better to take it away sooner rather than later if you can because the longer they have it, the more attached they will be and the harder of an adjustment. Hope you find something that works!