21 with pelvic & anal prolapse due to constipation, am I a good candidate or is it too late?

The first thing you need is a thorough pelvic examination to see what's going on with your anatomy and then determine the best way to improve your situation. Vaginal rejuvenation is not a treatment for any of the conditions you mentioned. See your gynecologist first. Then repost with an update.

Thank you for your questionConstipation will lead to hemorrhoids but It is unlikely pelvic or anal prolapse. If have two tunnels (vaginas) you can have a condition known as didelphus uterus in which you can have two vaginas.This can be easily identified by a pelvic exam with your gynecologist. The septum (vaginal skin dividing the two sides) can be removed. Regardless, there is excellent chance to be fixed and you are not a lost cause but, you do need to see a competent knowledgeable gynecologist to evaluate, diagnose and make a treatment plan. There is no procedure called "vaginal rejuvenation". It is the effect of any of a number of procedures that make the vagina more youthful so you need the specific procedure for your issues which can only be determined with a pelvic exam. 

I don’t think it’s too late, but it will not be advisable to do surgery on your pelvic floor until your anal prolapse and constipation has been fixed first; or it can be fixed at the same time. Your consideration is primarily functional not aesthetic- so you need a Colorectal Surgeon assessment and appropriate investigations first

Thank you for reaching out with your concerns. Based on the details you've shared, you are a strong candidate for vaginal rejuvenation procedures due to your age and specific symptoms. Here’s a detailed explanation of what might help:
Evaluation and Diagnosis:Given your history of severe constipation and the sensation of prolapse, it’s essential to confirm whether you have pelvic organ prolapse (such as rectocele or cystocele) or anal prolapse. A thorough examination will help determine the extent of the condition and guide the treatment plan.
Vaginoplasty with Pelvic Floor Reinforcement:
A vaginoplasty procedure can restore the vaginal anatomy by removing excess tissue, tightening the vaginal muscles, and reconstructing the pelvic floor. This aims to restore strength and normal function.During surgery, any prolapse (e.g., rectocele or bladder prolapse) will also be addressed. Strengthening the pelvic floor muscles and correcting any defects caused by chronic constipation will help ensure long-term improvements.Postoperative Recovery:
The surgery is typically minimally invasive, and patients often return home the same day or after an overnight stay.Recovery is relatively straightforward, with minor bloating or discomfort resolving in 1–2 weeks.Normal daily activities can resume after 1–2 days, while sexual activities are restricted for 4–6 weeks to allow complete healing.Prognosis:At your age, your body’s ability to heal is excellent, and with appropriate intervention, you have a high likelihood of regaining normal function and resolving your discomfort.
Please consult with a specialist to conduct a comprehensive pelvic examination and confirm the treatment plan. Early intervention can significantly improve both your physical and emotional well-being. Remember, you are not a lost cause—there are effective solutions, and we are here to help!