Hi Marcela,
I went and read your other post :) and while only you can decide what is best for you - here are my thoughts. (Nota Bena: I am 46, so we share an age bracket).
The Social Security benefits - will receiving his deceased spouses SS greatly impact his ability to retire? Will this income allow him to retire early (or at all)? It may be that, without it, he will have to continue to work well past retirement age. So it may be a strictly financial need to wait.
Which leads to a discussion of spousal financial benefits - on a purely financial basis, marriage offers security to spouses in the event of one's death. You can obtain that same financial security, without being married, through estate planning, wills, and life insurance benefits.
On an emotional level, of course, you want to be legally bound to him, and him to you, by marriage. And this is where is gets sticky. I, personally, feel, that at my age, if I found a mate, I would really not care about getting married. I would choose the financial planning and wills to protect one another and care for one another, but feel no need for the ring anymore in my life. But, with a 14 year old at home, my lifestyle choices are predicated on what is best for my son - not necessarily what I want.
If being married is important to you, then you need to closely look inward and decide if it is worth it, to you, to wait. Or to simply move on and find someone who is willing to get married sooner, rather than later. Is it possible to have a long (okay, really long) engagement to him? An engagement ring that is a promise of marriage may assuage your worries and symbolize his commitment to you.
As to worrying about what his kids will think, this one bothered me a lot. He needs to ask them. They are grown, no longer dependent on them, so it should really not be a concern if Dad gets married. I think the more important child here is your daughter- what does she think? What lessons about relationships do you want to teach her by your example? Talk to her, find out what she wants from, and for, you, her Mother. That may help you find your answer.
I hope you find the answer that works for you and your family.
Good Luck and God Bless