Im not a huge expert but i love my science youtube channels, but the reason why we look old is that our our DNA or our organ dna strands (something like this)/cells decay over time. The reason why we get old is because our body loses the abilty to generate newer cells to replace. Each new cell is worse than the last. So over time we get older. Think of it like how rumors start. You have the clear message the first person it spreads to. When that person spreads the message its slightly wrong. Then the next person spreads it, its even more wrong. And it just goes on like this til eventually it can't make the newer cells and we die or theres organ failure, or a mental disease occurs.
Also living to 122 is extremely rare and only 1 person got there while a handful of others gotten close. And that hand full is quite a literal meaning. Its like less than 10. Out of nearly 8billion people. But your line was the average life span is 140 this should mean that we have the potential to live older. While the current average life span for a male is about 75 and a female is 70 people do live to 100 fairly often. Thats 30yrs. So potentially in this universe you created people should be able to reach 170 years old with very few making it to 192yrs old.
So do you see why i am scratching my head at this. I have no problems with the milfs its just that they should be technically older. Cause again the explanation i used while quite broken is not entirely off. If we are getting to an average of 140 that means our bodies are doing much better in its cell/dna replication that its not decaying at the current rate which means they would look fairly younger at the ages you put down. In fact this is one way scientists are looking to tackle aging. Some are actually thinking dying of old age is actually not a natural process at all but more like dying from a disease. If we can slow down the decay or even repair the decay then death by old age would be nonexistent or extremely far off. (Its been a bit since i heard of this so how accuat i am is not great but this is the general gist)
Which brings me to the point that they just need an age bump to like 70. And yes our current logic says thats cougar not milf for your universe it would be a milf cause at 70 they would be considered middle aged. At 38 to 42 they should still be considered either young adults or just an adult much like how a 25yr old is considered neither young nor old. (Although with me just turned 37 a 25yr old is definitely young).
Thats all i feel like their ages needed to be adjusted or they needed to look younger.
Our bodies would mature at much the similar rate until we reach mature adulthood which is somewhere in our 30's. The postulation that aging has been slowed would not necessarily affect the maturation process. That means that those ladies who are in their 30's and 40's in this story now would continue to look like they are in their 30's until as late as their 90's or even later. The aging is slowed, not the process of human maturation. The way you pose it would affect humans all the way down to infancy, looking like a toddler at age 8-12 and not reaching puberty until sometime in one's 20's! Yet, in reality, our bodies would continue to mature at the same rate they do now, we would simply remain looking more youthful as we age more gracefully from that point of maturity.
There are examples of graceful aging even now. My favorite examples are Jacklyn Smith, one of the original Charlie's Angels on TV and my own dear mother. Ms. Smith will be 78 this year and still looks as if she is in her early 40's. She is a rather wealthy lady so she can afford all the special treatments that help her remain looking young but she hasn't ever had any cosmetic surgery, she just looks young because she takes great care of herself. My mother will be 87 this fall and still doesn't look a day over 60. She would appear even younger if not for her full head of silvery white hair. My mom's secret is the same one her elder sister passed on to her, Pond's cold cream every night and frequent use of moisturizing lotion.
Ishani, Alina, Marissa and Raegan all look to be in their 30's because they have just reached that point of maturity in their lives. However, with the longevity of humans in this current time and place, they will all continue to look like they are in their 30's for several decades yet to come. Outward appearance as well as internal health would remain stable for a greater length of time with the bodies new found ability to regenerate dead cells, well past the age of 100. I imagine that would mean that things like male pattern baldness, age spots, thinning grey/white hair, skin wrinkles and other signs we attribute to old age would be delayed until one reaches 110-120 or so while each new life continues to mature at the same rate it always has.
Umiko is in a different situation having Huntington's disease. I hope that she finds the advanced treatments available on Elysium in time to give her a longer life to enjoy life with her daughter. 
My friend, ask yourself, would you really want to look like a toddler at age 10 or wait until age 25 or 30 to enter puberty? Both are a resounding NO for me. Hahaha
So, I lean toward the maturation cycle of humans to remain much as it is now as would women's psychological reaction to aging. Regardless of how young they look, women will always feel the sum total of their life experience and feel old long before they actually are. "I'm old!", "I'm fat!", "Oh my God I have cellulite!", "Aw hell, I have stretchmarks!", "Aaaaah! A gray hair!" would still be heard from women even in the absence of any evidence that such things have occurred. It's just part of being a woman, I think.
I hope this makes sense and helps suspend your disbelief, my friend.
Adventure ever on, Phat
