In terms of frequency - I can definitely live with less sex than in my 20's. I mean, back then every other day and several times a day was great. Now, once a week is fine.
However, I find sex lasts MUCH longer now. I have more appreciation for the slow exploration and buildup, bringing him to the edge, and then letting things simmer before ratcheting up the stakes. Instead of the quick "getting off" that characterized my sexual goal when I was young, now play sessions that last for hours is the norm.
So, for me, sex is better now - though admittedly less frequent.