I don’t know what you are looking at for “older”, but I am 37.
Well, I don’t know if stresses are absent just because you don’t have kids. I don’t think there is a magical age where it all just falls into place though it is nice to dream 😉
As long as you are living, there are going to be challenges. That is part of life!
There are lots of things that can be “stressful” even without kids.
Some of it may be part of what you choose to take on (wedding planning), other parts of it are just the facts of life (like family and friends dying).
You or your partner may deal with serious illnesses or disability (and eventually, aging and all that brings health wise). I have had my own significant surgeries in the last three years or so to deal with hereditary risks that had potential to cause significant stress and do for some.
Or you may be seeing/helping your parents through illness, disability, or just aging. I am watching my mother die of terminal cancer now. A childfree friend of mine is dealing with both his mother dying of cancer, and his father needing extra care as he ages and him having to be there to help out. It is very stressful for him.
Unexpected expenses still arise. You can expect those for the rest of your life. A blown furnace, a car accident, emergency veterinary bills. Sorry, but there is no homefree from that!
You will likely even when you have a job have stress at work, or maybe face the stress of downsizing, a poor economy, or losing your job. Depending on what you do, there is always also more schooling, training, and so on which can be stressful.
I don’t really think about if it would be “harder” with kids, either, because I just don’t compare. I am just glad I don’t have kids! However, I am cognizant that having kids would have its own set of stresses – particularly stressing about them.
I think I do have the maturity and experience to know that “I will get through this” though when I am going through a challenging time, because I have been through it (or worse) before. I don’t consider life “stressful”, though there are stressful moments. It is just life and it has better times and more difficult times.