You may not be as young as you feel, but research has found that a positive attitude may delay the ageing process.
Is ageing inevitable?
The University of Texas found people with an upbeat view of life were less likely than pessimists to show signs of frailty.
The researchers say their findings suggest psychosocial factors - as well as genes and physical health - play a role in how quickly we age.
Their work is published in the journal Psychology and Aging.
The Texas team carried out tests on 1,558 older people from the Mexican American community to examine whether there was a link between positive emotions and the onset of frailty.
At the start of the seven year study all the volunteers were in relatively robust good health.
The researchers assessed the development of frailty during the study by measuring the participants' weight loss, exhaustion, walking speed and grip strength.
They found that those people who had a positive outlook on life were significantly less likely to become frail.
The researchers said more research is required to pin down why there should be a link.
But they speculate that positive emotions may directly affect health by altering the chemical balance of the body.
Alternatively, it may that an upbeat attitude helps to boost a person's health by making it more likely they will be successful in life.
Lead researcher Dr Glenn Ostir told BBC News Online: "I believe that there is a connection between mind and body - and that our thoughts and attitudes/emotions affect physical functioning, and over all health, whether through direct mechanisms, such as immune function, or indirect mechanisms, such as social support networks."
A second study, published in the same journal, also suggests that physical performance can be influenced by mental attitude.
A team from North Carolina State University asked 153 people of different ages to carry out memory tests after being exposed to positive and negative words to describe stereotypes about ageing.
Negative words included: confused, cranky, feeble, and senile, while positive words included: accomplished, active, dignified and distinguished.
The results showed that memory performance in older adults was lower when they were primed with negative stereotypes.
In contrast, there was much less difference in performance between young and older adults primed with positive stereotypes.
The researchers say their findings suggest that if older people are treated like they are competent, productive members of society, then they perform that way too.
Lead researcher Professor Thomas Hess told BBC News Online: "There may be social situational factors that can have a very strong impact on older adult memory performance.
"It may be very subtle. People may pick up on negative cues in their environment which suggest they are not up to it, and as a result will not perform well.
"It may be that if people can suppress these negative thoughts that they will do much better, and that a positive attitude can promote effective functioning."