Is it normal for husband and wife to be so horny for each other?

My wife is 12 yrs. my junior, an RN by profession with a legal degree and former Las Vegas show girl with the same freshness she had when we first met. Still pretty and after 3 kids and more than 20 yrs. of marriage just 6 pounds over weight but it all went to my favorite spots on her. If I didn't believe in God I'd be on my knees worshiping her behind. The way her ass sticks out back there with a defined upward slant lets you know she works out for the woman is still a danger to men in motion when she walks down the street. Our kids think we're always on something because we don't act like their friends parents as older married couples but boy friend and girl friend and with our kids away we have grown more sexually active because we have our privacy as we did before the kids.
Yesterday my wife asked me to meet her for lunch at her job after I came home from a 5 day trip out of town. She works in the hospitals legal department now and is in no rush as she was as a supervising RN doing a nurses duties, so while eating lunch in the hospital cafeteria she whispered in my ear that she didn't ask me here just for lunch but to fuck and she wasn't fooling. When we went to her office she locked the door but taken off guard I wasn't quite ready for this here but when she dropped her dress and put her panties in one hand to my nose, the other around the nape of my neck pulling me down on top of her to the couch she said, "now smell my pussy I've been carrying your cum in me for 5 days and I know it smells dick hardening good now don't it? As usual as soon as I smell that moist hot pussy that scent made me excited with passion and my joint was oak hard at attention. I took about 2 mins. savoring that good pussy smell, kissing her thighs and licking her clitoris before she said almost breathlessly with passion, "when you put it in rub the head up and down the lips of my pussy like you do a few times before you go in." She laid back gapping her thighs and got into her position where she could give me 100% pussy and get all of my hard dick into the fit and I said, " Hi, sugar I'm home and it sure gets slippery when its wet" with synchronized motion we played lovers as my deep penetration going in on the down motion and coming up and back while acting like a shaft my joint rubs up against her clit where she countered my motion to put it right there in every fluid dick hungry motion she made. We normally do our rolling and riding, slipping and sliding for about 10-12 mins. where she gets 3-4 orgasms and then I let it go but I hadn't had my wife for 5 days and I stayed in but working it harder while she moaned in frenzied excitement then said, "Oh, you're gonna give me some more, get it daddy." There has only been 2 other times in my life that my passion with her took it on until I had another orgasm without recuperating before I went back in. She has got some good pussy.
We finished and got decent but before we left the office I told her to lay on her stomach for a minute as she did I lifted up her skirt and rubbed my face in her ass she sprayed the office knowing her aphrodisiac pussy smell was obvious to the nostrils. That woman knows how to turn my passion on and make my desire for her almost insatiable. While friends my age have declined in their sex lives some complaining about their wives other visiting prostitutes on the sly my wife and I are still hot for one another.
When do I start to decline in my interest and love for her pussy? She still has her periods and that time each month where she is in heat and that time is now. She goes into her slut mode and I love it, being playful when at the right moment she throws her dress over my head knowing the that passionate pussy smell has become more pronounced for its no one but us here now and my dick is a bit sore but that don't stop it from getting hard. The scent of her cum filled pussy is like a feminine delicacy to me that gives me a sexual prowess befitting an unselfish lover. My wife calls me her dixman because I give her pussy a black eye. Is this normal?