I am 54, female. I have underbite/crossbite as per pictures (Photo)

You definitely need orthodontic treatment to correct your bite. Whether it can be done with orthodontic treatment alone, or in combination with a jaw surgery, called orthognathic surgery, needs to be determined by your orthodontist. Please see an orthodontist in your area. Yes, it is safe to have orthodontic treatment, or surgical orthodontic treatment at your age if you have good bone support for all of your teeth. There are many more patients that are much older than you who can safety undergo orthodontic treatment.

Hello, There is a considerable amount of information that is required to make a proper diagnosis and treatment plan. Given the pictures you have provided, it would appear that you may have a skeletal discrepancy between your upper and lower jaw, hence why your lower teeth are more forward (underbite). This can certainly be corrected, and I would recommend that you look at options to do so.  Your treatment will involve upper and lower braces (with or without the need for extractions of certain teeth), followed by orthognathic surgery (jaw surgery).  This type of treatment typically takes anywhere between 2-3 years. Please seek out the advise of an orthodontist (specialist) and they will be able to do a full exam and give you all the necessary information regarding your particular case.