Happy Birthday to your dad, Belle! How wonderful. My dad will be turning 100 years old in December, my Mom 98 in November, so I know how precious this time together is.
Off of the top of my head I have:
"The best of today is sharing the gift of time with you, Dad! Cheers to you and your young at heart way! May we continue to cherish your special journey together for many more years to come! Here's to our rock! Congratulations on 90 years young! HAPPY HAPPY BIRTHDAY to you, my kind, and handsome father. I love you!"
That's what I would say to my dad, however, you may incorporate that with adding in your own sentiments. Use it all, part of it, or not at all. Definitely do it your way.
Here's to embracing this special moment celebrating your dad, with others who love him too. Have a blast, Belle! : )