I met my husband when I was 18 and he was 28. He proposed within 2 months. My parents wouldn't give consent, said I was too young, the age difference was too great, it would never last.
We married as soon as I was 21 (the age of majority at that time) and have been married for over 45 years.
So, 20 and 25? Pah. Nothing.
Maybe your 3-year wait helped your marriage last this long ? I mean, you had time to think about it and get ready, whereas wedding after only a few months might have brought some desillusions...
Besides, it's kinda obvious age gap doesn't always mean the same : a 3 year older brother seems soooo much older and wiser when you 10 than when you're 30. When you're 18, 21 or 25, you're at a different stage of life, your "path" is more or less defined, and that does matter, I think.