Ultherapy or Exilis for slightly sagging arms and knees? (photos)

With your degree of skin laxity you will not see a significant benefit with Ultherapy or Exilis. You may want to consider something like ThermiTight, however, realistically non-surgical treatments will provide subtle improvement. Hope this helps.

To be honest, Ultherapy has not been approved by FDA to treat arms and knees as of yet. I now that some doctors used a 4.5mm transducer to work on those areas, but you have to understand that safety of this procedure and following results have not been evaluated.

Exilis is not going to be your best treatment option for the areas you are interested in tightening. I would suggest Thermitight or Ultherapy. Thermitight can provide amazing results, especially when combined with Ultherapy. I would also recommend, along with your in-office treatment, starting an anti-aging skin care regimen to stave off aging changes and improve your skin-health. A retinol body lotion (Replenix makes a great one!) and SkinMedica TNS Recovery Complex are good choices for restoring elasticity to your skin and reversing some of the aging changes. Most importantly, don't forget to use your sunscreen. 

As a healthy 63 year-old who has enjoyed lots of sun in AZ, you have permanently lost youthful elasticity and no non-surgical skin tightening treatments can overcome that to any degree where they are worth doing. Best to just stay fit and continue to enjoy a healthy lifestyle.