Some say we have a greater appreciation of parenthood because we waited longer to enter this stage of life. I don't believe the sense of happiness, pride or unconditional love I feel for my children is any different than a younger Dad's. I just throw out my back more often.
As the calendar took me into my 40's, I fell in love and suddenly, children entered the discussion (though I worried about being called "Grandpa" by mistake).
As an older parent puffing along in the early laps of child rearing, I can offer one piece of advice: Enough with the math. Resist calculating your decline against the kid's milestones.