Eddie- If you are raising LaMancha and NUbians, they should be 80 pounds by about 8 months. Once 8 months old and 80-90 pounds if they are cycling consistently they are ready to be bred. Your full size breeds come into heat roughly August - January. As Sara said if your goats are 11 months and only 75 pounds , you might want to wait until next fall to have them bred. This will give you a chance to get them wormed and get all of their vaccinations up to date and get some more growth on them.
If you breed this late you'll be having June kids, which is not ideal for many reasons.
Eddie you read here Ideally before you buy, but we can help you now. The person you purchased from is very new herself, and without help you just can't raise out robust kids. Whe new you are still in the trail and error stage yourself, or what you know is from the internet or worse...books or vet and not from practical experience. Vicki