Thoughts on Having a Child at College

Am I the only one who reaches this age (46) and stage of life who doesn't feel like a real grown-up yet? At what point do I get the self-assurance that all those other people (my age and even younger!) seem to have?  Are they all faking it?
What have I been doing wrong all these years, that I still see myself as 20? And I think that people see that way.
How completely delusional is it of me not to realize that kids, teens, 20-somethings, even 30-somethings see an old guy when they see me?  At some point my mental image of myself needs to catch up with who I am. I think I would have a lot more self-confidence if I did.
This is not to say that I am super-smart, filled with the wisdom of the ages and amazingly talented. I not saying that I need to go on an ego trip here.  I just need to realize and act on the lessons of life that I did not have the benefit of when I was 14, 20, 30, 40.  It isn't possible to understand this stuff until you experience it.
It may be that I have spent so much time in my life being around older people (I am the youngest child by 7 years, my dad was 46 when I was born, for a couple of examples), being treated like a kid ("Billy the Kid") that that image has been fixed in my psyche.
Maybe I need to recruit a cadre of young people to bow down to me (figuratively), seek my advice, be impressed by my wisdom, show me great respect, and, oh yeah, get me things so I don't have to get up.
Any volunteers?
Anyway, as to the fact of life that my oldest child has left home and is in college - it is a difficult thing to realize that this new phase of life is irreversible.  This is one change that cannot and will not be undone.
She is having the time of her life - and I, I am stuck mourning (maybe too strong a word, but it is all I could come up with) the loss of her presence, her wit, her hugs, and bunch of other stuff.
She has replaced us with school, and new friends; we've replaced her with...
well, there's an empty chair at the dinner table, one less car in the drive, and an empty bedroom.
Somehow, I think she got the better end of the bargain.