I personally witness that my friends who are married experience faster biological aging than those who are single. Has anyone had a similar experience? Or what is the truth?
https://www.quora.com/Why-do-people-start-looking-older-after-few-years-of-marriage
My guess is the massive loss of sleep that can happen when you have kids.
Been married for 49 years this month. Been a couple for 52 years. Four kids! lots of lost sleep and stress when we were younger.
We are both in the top 100 (out of over 1,200 participants) of the Dunedin Pace | Rejuvenation Olympics you can search on “Joan Matheson” and “Stephen Matheson”
That is a good question so I asked my friend https://www.asklongevitygpt.com/ this question “do married couples experience faster biological aging”
Here is the Conclusion
The impact of marriage on biological aging is not straightforward and can vary based on the quality of the marital relationship and individual behaviors. Here are some key points:
Overall, the quality of the marital relationship and individual health behaviors play a crucial role in determining the impact of marriage on biological aging.
I don’t think marriage ages you faster, but stress does. It’s most likely important to find the right partner. Having children is certainly hugely a hugely stressful event.
I guess it depends on who you marry. I was married to a wonderful woman for 53 years and I definitely believe she has helped me live longer because of the companionship and guidance she gave me on living a good life.
“A major survey of 127,545 American adults found that married men are healthier than men who were never married or whose marriages ended in divorce or widowhood. Men who have marital partners also live longer than men without spouses; men who marry after age 25 get more protection than those who tie the knot at a younger age, and the longer a man stays married, the greater his survival advantage over his unmarried peers. But is marriage itself responsible for better health and longer life?”
“Men who never married were more than twice as likely to die within about five years after a heart failure diagnosis compared with women of any marital status or men who were previously married, according to a study presented at the American College of Cardiology’s Annual Scientific Session Together With the World Congress of Cardiology.”
Marriage and Men's Health - Harvard Health Publishing - Harvard Health.
Devil’s advocate, eunuch generally live decades longer than average men, and clinical trial also shows castrated dogs live longer than untouched dogs.
The same to women, pregnancy makes women aging faster, reproduction cost dearly even though it’s a necessary mean for specie’s survival…
If marriage is only about accompany, why not get a dog? The marriage can be a social security to support each other financially or physically but it means one of the couple must sacrifice.
Married people do gain weight more readily. I wonder how much of the appearance of aging comes from that?
I do think that marriage ages you faster. It’s very difficult, if possible at all, to find the right partner. Marriage is especially stressful for those who need more space and time alone. Stress accumulates and eventually kills. I have so many examples of that.
I’m an example. Though not exactly anti-social, I am a bit of a recluse. Even so, I acknowledge that the love of a good woman is probably the greatest gift that luck and life can bestow on a man.
You’re probably right in that finding the right partner is a huge challenge, but a successful marriage may have more to do with people’s emotional intelligence and communication skills, and that goes for both sexes. I suspect most people don’t want to put the work in, because that means facing yourself and compromising. The divorce rate says it all, and it’s something like 50 percent of marriages end in divorce, and divorce is one of the most stressful life events you can go through. Interpersonal relationships are probably more complicated than aging. Ok, I retract my previous statement. Yes, marriage ages you faster. 
I think it can be both ways depending on many individual factors.
I thought married people live longer, recall reading that somewhere. I know I have, tempering my wild and crazy days, being married, kept me from joining the “27” club (probably).
I would, but I don’t want to have to pick up their shit when we go on walks. Hopefully I wouldn’t have to do that with a girlfriend or a wife.
I’ve had years (the for worse part) where I’m pretty sure it aged me faster and years where it probably helped slow things down (the for better part). I think it comes down to being on the same page and having similar goals and priorities. One thing’s for sure I don’t plan on trying again if something happens to my husband. 
Between 65 and 85 years, married men and women had a longer TLE and ALE than unmarried men and women. For example, at 65 years, TLE for married men was 18.6 years, 2.2 years longer than unmarried men, and ALE for married men was 12.3 years, 2.4 years longer than unmarried men.
A dog is a wonderful addition to a humans life. And the dog likes it too. The human-dog partnership has been bred into both species (I believe). It isn’t a partnership of equals, unlike a husband-wife partnership. But both are partnerships where combining differing strengths make the team stronger…more than the sum of the parts.
A dog can’t drive one to (say) doctor’s appointments, but married couples can drive each other when each one needs it.
…I wouldn’t be so sure about that 
One thing (OK many things) I’ve learned about being married is the compatibility thing. I’ve seen very incompatible people together and it’s painful to see and be around so it must be painful to live. It makes sense that this type of relationship would have a negative impact on longevity and health overall.
I don’t know how but I was truly lucky to find my perfect mate when I was 15 and marry her when I was 19. Today that is considered heresy in finding a mate, you need to search, experience, test, evaluate, date more, focus on your career, etc.
Loyalty, devotion, kindness, caring, all the things that make “love” an action word are key to living in a healthy long term relationship.
Love as an action word is what we taught our 4 kids. But it is not easy (it wasn’t always easy for us) as I watch them grow in their relationships. The funny thing is, they see us now through their adult eyes and I think they are starting to understand that love is an action word.
I know that my life mate has a huge positive impact on my health and longevity.
Wow, you are lucky! At 15, my perfect mate was my dog.
I think pets are a better substitute for children than they are for partners/mates. You can still scold them and send them to their rooms - don’t try that with your wife.
I personally prefer a cat, because they know how to bury their shit and they’re more independent (like me). But unlike a wife (or husband), you can always throw them outside if they’re getting annoying.
And I don’t think having a pet ages you faster…unless it’s like @DrFraser 's dog. He was asking for advice here on how to get rid of him!!!