Factors that affect libido
Endogenous compounds
Libido is governed primarily by activity in the mesolimbic dopamine pathway (ventral tegmental area and nucleus accumbens). Consequently, dopamine and related trace amines (primarily phenethylamine) that modulate dopamine neurotransmission play a critical role in regulating libido.Other neurotransmitters, neuropeptides, and sex hormones that affect sex drive by modulating activity in or acting upon this pathway include:

Testosterone (directly correlated) – and other androgens
Estrogen (directly correlated) – and related female sex hormones
Progesterone (inversely correlated)
Oxytocin (directly correlated)
Serotonin (inversely correlated)
Norepinephrine (directly correlated)
Acetylcholine

Sex hormone levels and the menstrual cycle
A womans desire for sex is correlated to her menstrual cycle, with many women experiencing a heightened sexual desire in the several days immediately before ovulation, which is her peak fertility period, which normally occurs two days before and until two days after the ovulation. This cycle has been associated with changes in a womans testosterone levels during the menstrual cycle. According to Gabrielle Lichterman, testosterone levels have a direct impact on a womans interest in sex. According to her, testosterone levels rise gradually from about the 24th day of a womans menstrual cycle until ovulation on about the 14th day of the next cycle, and during this period the womans desire for sex increases consistently. The 13th day is generally the day with the highest testosterone levels. In the week following ovulation, the testosterone level is the lowest and as a result women will experience less interest in sex.Also, during the week following ovulation, progesterone levels increase, resulting in a woman experiencing difficulty achieving orgasm.
This is in sharp contrast to girls where virtually none are engaging in masturbation before age 13, and only around 20% by age 13–14.People in their 60s and early 70s generally retain a healthy sex drive, but this may start to decline in the early to mid-70s. Older adults generally develop a reduced libido due to declining health and environmental or social factors. In contrast to common belief, postmenopausal women often report an increase in sexual desire and an increased willingness to satisfy their partner. Women often report family responsibilities, health, relationship problems, and well-being as inhibitors to their sexual desires. Aging adults often have more positive attitudes towards sex in older age due to being more relaxed about it, freedom from other responsibilities, and increased self-confidence. Those exhibiting negative attitudes generally cite health as one of the main reasons. Stereotypes about aging adults and sexuality often regard seniors as asexual beings, doing them no favors when they try to talk about sexual interest with caregivers and medical professionals. Non-western cultures often follow a narrative of older women having a much lower libido, thus not encouraging any sort of sexual behavior for women. Residence in retirement homes has affects on residents libidos. In these homes, sex occurs, but it is not encouraged by the staff or other residents. Lack of privacy and resident gender imbalance are the main factors lowering desire. Generally, for older adults, being excited about sex, good health, sexual self-esteem and having a sexually talented partner can be factors.