Not always. My cousin and his wife married late in life (right about 40), then had two children in 5 years. They were a healthy couple with no reason to be concerned starting a tad late. When the youngest was two, his wife started to change, and things deteriorated rapidly. She was eventually diagnosed with an early onset rapidly progressing form of dementia. Their healthy dual income disappeared. They had major medical bills. Not only did they need child care for two very young children, but around-the-clock care for an adult as well. Life has not been kind or easy for them. Her health at 40 was no indication of what was to come.
I'm not saying the OP shouldn't adopt a child. BUT, I think age has to be taken into account. It's a fact that with age you have an increased chance of health issues - regardless of how well you have taken care of yourself.