## 1 Introduction  
Since the beginning of human civilization, plants have been used in virtually all cultures as a source of remedy for multiple health conditions, as documented from the centers of civilization. They comprise a brilliant source of exogenous antioxidants, whose activity ranges from extremely slight to very great [1,2]. Indisputably, these natural antioxidants may act as reducing agents, free radical scavengers, singlet oxygen forming and pro-oxidant metals quenchers, localized O\({}_{2}\) concentration reducers, endogenous antioxidant defenses boosters, and avoid damage in repair systems, or any combination of the above. Also, they protect against oxidative stress, which in turn helps in maintaining the balance between oxidants and antioxidants levels [3].  
Interestingly, reactive oxygen species (ROS) have been considered to be the uninvited companions of aerobic life ever since molecular oxygen was introduced in our environment about 2.7 billion years ago [4]. Under steady-state conditions, ROS molecules are scavenged by various antioxidant defense mechanisms [5]. In this sense, the antioxidant potential of plants has attracted a great deal of attention, because increased oxidative stress has been reported as a major contributing factor to both the development and progression of aging and numerous life-threatening disorders, including neurodegenerative and cardiovascular diseases [6,7].  
Plants possess miraculous antioxidant effects because of their high oxygen exposure physiology. In fact, plants may have more sites of ROS generation. Therefore, they could evolve more proficient non-enzymatic antioxidant systems than humans [1,8]. Plants synthesize several enzymatic and non-enzymatic antioxidants to avoid free radicals' toxic effects, in addition to be able to synthesize and accumulate a wide variety of low and high molecular weight secondary metabolites, which play important roles in ROS metabolism and effectively avoid the uncontrolled oxidation of essential biomolecules, thus, acting as antioxidants [1, 8, 9].  
There is a broad diversity of naturally-occurring antioxidants found in plants, differing in their composition, physicochemical properties, site, and mechanism of action. The major antioxidant plant secondary metabolites are phenolic compounds, and they can be divided into five general groups, namely, phenolic acids, flavonoids, lignans, stilbenes, and tannins [10, 11, 12]. Briefly, they provide protection through scavenging numerous ROS, including hydroxyl radicals, peroxyl radicals, hypochlorous acids, superoxide anions and peroxynitrite [13]. Particularly, the antioxidant activity of polyphenols in cardiovascular diseases, such as the activity of hepatoprotective, anti-carcinogenic, antimicrobial, antiviral, and anti-inflammatory agents, has been broadly described [14, 15]. In fact, anthocyanins play a key antioxidant role in plants against ROS-generated abiotic stress, such as in the case of ultraviolet light and extreme temperatures [16, 17]. They also inhibit chemically-induced cancer and turn off genes involved in proliferation, inflammation, and angiogenesis [18]. Also, these secondary metabolites are known to prevent a key step in atherogenesis and are more potent antioxidants than vitamin C [19].  
Moreover, a meta-analysis of epidemiological studies has shown that carotenoids act protectively against head and neck cancer [20], while other studies have suggested that carotenoid-rich diets appear to have a protective effect against Parkinson's disease (PD) [21] and prostate [22] and breast [23] cancers. In this sense, the objective of the present review is to provide a detailed overview of plant-derived bioactives and their effect on age-related disorders. Specifically, the role of phytochemicals as antioxidants and pro-oxidant agents is carefully addressed, as is their therapeutic relevance in longevity, aging-related disorders, and healthy-aging promotion. Finally, an eye-opening look into the overall evidence of plant compounds related to longevity is presented.