I started working out again this year I am in my early 40's what i made sure to do is not to use all the heavy weights start of low weight and do reps.
Way to easy to pull muscles as you get older I am working out between 4-6 days a week depending on week and stayed pretty much injury free.
Listen to your body is my other suggestion by all means push yourself but make sure not to do it to quick or to much at once. I started off two days a week went to three and ramped up as my body felt stronger.
"It is the duty of the patriot to protect his country from his government."