Where do you draw the line? = Where do you set the limit to what is acceptable? (And acceptable to whom?) Regarding your question, the potential answers are more interesting than "rephrasing the question". The.question is perfectly fine. There is no need to rephrase it. The answers are necessarily subjective, but there are these aspects: 1. physiological limit for a woman due to menopause; (or the ethics arguments for and against surrogacy) 2. what child psychologists say about the impact of a 50+ age gap between parents and child; 3. retirement and finances.