Dont feel dumb about posting it, but umm.. yes. this is very different for me. But this could be because your family might be completely different to mine -
Do you guys sit at the table for dinner? (we don't)
Is there some type of patriarchal thing within your family? (there isn't in mine) for example, is your dad seen as the "head"?
Also, you said "I was the baby of the family so that's understandable". This isn't understandable to me at all - your age is irrelevant in my family, age does not define quality or character or worth - all are equal where I come from, and all have equal say (well.. almost!). If age was relevant in your family, he wouldn't STILL be serving you last.
But all families are different and that's ok. As long as everyone has equal ability to give their input and gain respect from ALL others, including the "head". Which brings me to my next question......
If this bothers you - have you said anything to them? I mean just in passing, joking, messing about as families do. If this was continually happening to me for example, after the first few weeks of noticing it, I would say "how come we always serve in the same order?" or "how about we serve anticlockwise, itll make things easier" (then sit in different places each time and you wont always be last). If it was my family, Id just say "hey, me first for a change" lol and that would be perfectly ok.
If you haven't said anything... why not? Is there a communication or emotional issue with your father?
If there is, theres the answer as to why you have a problem with such a small thing. Its not small to you because there are underlying issues. If so, its the underlying issues you need to deal with, not the order of service at dinner.
I could be way off, but it just seems to be something more than "low self confidence"... I mean decades of being served last isn't a coincidence.
Someone serving someone last consistently in our family, would really be seen as a show of dominance by the father - trying to push the other person down consistently. It would actually be seen as passive aggressive abusive behaviour.. NOT even remotely ok. Clearly as you've mentioned its not about age... it seems to be about respect and rank... and youre not getting either.
Could be wrong... just being honest.