26 year difference...

I need some advice!

I am 25, been married for a year and DH and I have been ttc since we got married. I am also an only child.

I just found out that my dad and his wife are expecting a baby in a few months. That will put us at 26 years difference in age. More than anything I'm shocked. Has anyone else been through or are in a similar situation. How do I get through something so strange??