As long as you educate yourself and know what you are doing you can do it at 90 without any problems. It is the stupid people that do it wrong and make problems for the people that do it right. watch this video but let me preface this before you watch it.
Even though it is an informative video it is by all means not a end all subject. It misses allot of points that a person needs to know before they start. One needs to know what he is putting into his body, what it is going to do and he needs to know what side effects to look for and what to do if the side effects happen. He needs to know how much and for how long. then he needs to know what to do after he finishes a cycle. All of the things I said are very important. anyone that does not have full of everything I mentioned does not need to ever pick it up.
http://www.youtube.com/watch?v=z0LEj8IPHGU
watch the video and do a search and you will see this is not the first time this question has been asked.
In my opinion if done right it would be wise do do it as apposed to not doing it.