When I was young I could curl my body weight. I weighed 125 when I was lifting at the age of 18. My strength to weight ratio was very high. I can't even come close to that anymore. As far as being safe yes it's safe however it's usually impractical. I was very "strong" in my upper body, however I was not well rounded. No lowerbody development and very poor stretching ability. If you focus on one thing you can always increase it to crazy numbers but I would shoot for an all around fitness level.