I am 40 and it has been slow. I expect it though since I am older, but just like the younger folks it will vary from person to person. I have been on T for 3 months now and there have been some changes. There were changes within a few weeks but nothing super drastic.
Libido increases, areas I had facial hair have a bit more hair. I had to shave daily before, same now. The hair that did not grow fast before is still on the slower side. My legs are becoming thicker and my feet must be getting a bit bigger to because I went to put on my tennis shoes yesterday to work out and they were borderline too small. I have not worn them in a few weeks, maybe a month. I have been wearing that size for most of my life, so I know it was not the shoe. I always buy the same brand/size and this was not a brand new pair of shoes. My voice seems a tad bit deeper also, but still not too noticeable of a change. I have a pretty neutral voice anyway until I raise the tone, then goodbye any passing attempt I had.
So yeah, they happen slower, but I don't think it is so slow it can not compare to younger guys based on what I have read on other threads. Also depends on how much you are taking. I am taking 2/3 full dosage weekly, and should be moving up to full dosage in 3 weeks when I go to my next apt. as long as my blood work comes back ok. Than changes should be more rapid.