Oral sex on women is physically easier than sucking (not that I have ever sucked), because you lick and rub, which is not too strenuous. Every woman is different, some like it soft, some medium, some hard, some on different parts of their clits and so on. With a new partner you have to experiment a bit and read her body language to get it right. With a long-term partner, you should know exactly what to do.
I suspect the 30-something women who don't orgasm may be married to men who haven't had so many prior partners, and don't really know what to do! The other thing that women CAN do is show and tell. Don't expect inexperienced men to know, because we all gotta start somewhere. I had a woman show me with her finger what she wanted me to do, and I duplicated that with my tongue and it worked. From then on, I had success with almost every girl I had sex with.