That sounds really hard OP, and I am sorry you are battling past trauma.
It’s tricky because much as you undoubtedly love each other you have different realities to juggle.
Moving in together / getting married is fraught if it is because you fear to be alone.
Also, to be truthful, in his situation I would be cautious / thoughtful about actually marrying or what that meant for my Dc.
Whereas you run the risk of retirement with someone much less energetic than yourself, he is in the position of contemplating dying maybe 20 years before you, and running the risk of seeing is Ds receive no inheritance, or else leaving you, his loved wife, vulnerable.
All this can be sorted, you just have a few challenges to take account of.
Are you confident that he talks openly and honestly with you about all these factors…. Teens, money, age difference, your trauma, anything affecting him, retirement plans, home ownership, Wills, how you each express commitment, importance of marriage… anything and everything?