So here are some facts that you might need to know:
Puberty's totally over (thank gawd), and your organs have reached their adult size. Except, that is, for your labia majora, the outer "lips" that enclose the rest of your privates. Don't be shocked to see these looking slimmer. As you age, subcutaneous fat, including that of your genitals, decreases.
In your 30's
The hormone shifts that come with pregnancy or aging can cause your labia minora, the "inner" lips that encircle the clitoris and vaginal opening, to darken in color. So you can relax if, on your next self-check, it's like 50 shades of (mauve-ish) gray down there.
The Big Stretch
The uterus balloons to watermelon proportions during pregnancy—then shrinks back down within six weeks after birth. Some 32 percent of women in the US now deliver by C-section, sparing their vag opening similar stretching (though their surgery scars can ache or tingle for years).
In your 40's...
Though a woman's egg supply dwindles rapidly in her early forties, she still ovulates and (sigh) gets her period. Cycles are a bit shorter though and tend to peter out by age 51—i.e., menopause begins. Your body puts the kibosh on fertility 5 to 10 years before that.
Your repro organs are supported by a hammock of tendons, tissue and muscle. Extra pounds, aging, or years of high-impact workouts can loosen this pelvic floor, straining organs and causing bladder leakage or a "heavy" feeling down below. Your move: Kegel exercises. Lots of 'em.
Lower estrogen levels affect the vagina's acid-alkaline balance, which can spur inflammation—along with thinning and drying of the vaginal walls, which can cause itching, burning, and redness. Silver lining: regular sex can prevent this atrophy (hop to it!).