looking back to what I was like in past decades, I would say I'm much more confident - a huge difference between me now and when I was younger is that I have much greater capacity to navigate the world and its challenges. Being older is great that way, even if it required lots of stressful life experiences to get here.
The other main benefit that came to mind is the financial stability - being able to benefit from the long-term planning and goals I set for myself allows me to feel more safe and secure, and gives me more freedom than when I was a paycheck away from eviction.
I asked my partner what her thoughts were on this question, and she agreed she is more confident now. She also said being older the sex is better, as you learn what you want and feel more secure with your partner.
She also mentioned not dating is a relief - having settled down with someone for the long term and feeling secure this relationship will last (and not always questioning if this is the right person, whether compatibility and trust exists, etc.) is a big relief.
Relatedly, she described the stress of her male friendships always trying to turn into dating, and now that isn't a problem.
She also mentioned that confidence and the ability to stand up for herself, and even make eye contact, are all benefits she has gained with age.