Spaw, my step-dad is 64 now. My mom passed away in 1995 at the age of 55 from smoking and she was older than he was.
I can actually tell you when I realized that the man who married my mother was not just a guy in the house but my "dad." I was very ill with a bout of shingles in my eye (I've had them since I was 12 and that was about when this realization took place). My dad was upset to see me in such pain and he couldn't understand why the doctors couldn't do anything for me, so he took off from work and took my to the doctors himself. He watched as I tried to deal with the pain of being examined (a lot of bright light, which hurts especially bad), and then he practically begged them to do something for me... actually he did beg them. They told him what they had told my mother, there was nothing they could do, the medicines available had no effect at the time. So, he helped me back into his car and I sat hiding from the sun and crying from being tired and hearing yet again that there was nothing to help me. He drove for a while and then he said and asked me to hang in there, and then being new to this "dad" thing he said, "Hey, I know, let's go to McDonald's for an early lunch!" (he knew I loved McDonald's Big Macs at the time). I realized then that I needed to pull myself together and his kindness and worry of me gave me the strength to do that. So, I swallowed the pain, wiped my face, and went and had lunch with my dad. From that day on, he was part of my family.
Thanks for reading this and asking, Spaw!