I am wondering what Bible scripture references you are referring to when you say, "the gospel promises us eternal youthfulness and beauty." I am familiar with the scriptures that tell us about no more pain, suffering, etc. but have never heard scriptures that promise eternal youthfulness and beauty.
1 Corinthians 15:53 says, “For this perishable body must put on the imperishable, and this mortal body must put on immortality.”
The source of ugliness is evil and sin. So, since our resurrected bodies will be untainted by evil and sin, they will be perfectly beautiful, as God intended. A resurrected woman’s beauty won’t conform to our cultural standards of beauty characterized by thinness and sexualization (as personal beauty has been defined currently by sinful people in a sinful world), but she will be far more beautiful than any supermodel.
Beauty flows from godliness (1 Peter 3:3-4), and in Heaven we’ll all be more godly than we’ve ever been before. Our resurrected incorruptible bodies will be unmarred by sin. We will then see beauty for what it really is and every person will possess it uniquely, as God has made each of us unique and cares greatly for us (Matt. 10:29-31).
We will have eternal youth in the sense that our bodies will no longer decay as they do now (2 Corinthians 4:16). This isn’t eternal immaturity, but eternal vivacity.
Julia (Stager) Mayo holds a Master of Arts in Biblical and Theological Studies from Western Seminary. She was previously part of the Eternal Perspective Ministries staff, and still does occasional research work for Randy Alcorn.