How do you know when it's time to get false teeth?

see a dentist. The decision to get full dentures depends on the condition of your teeth, what the dentist can do and what you want. If there is insufficient bone to support your teeth or they are decayed beyond repair then removal is the only option. I would urge you to see a dentist and try to keep as many teeth as possible.
Listen to dentist. I would have a couple of consultations on options other than dentures., too. I would also recommend that whomever is doing the treatment- dentures or otherwise, you must feel comfortable with the dentist and his/her staff.
See your dentist... I would have a nice evaluation by a dentist. The dentist would best be able to determine when is the best time. The answer is not always so clear. However, please see your dentist.
Age 49? People lose teeth for a variety of reasons, but primarily due to poor home care and infrequent visits to the dentist. Often, people take much better care of their car then their teeth. It is important for you to see a dentist to perform a thorough examination and take radiographs (x-rays) and then to determine the best treatment for your situation.
Dental Examination. You need to have a dental examination, with complete set of x-rays. That is the only way to determine the health of your remaining teeth. The dentist should be able to present treatment options.