First, have you confirmed that this guy is single? Second, he may have been texting with you for old time's sake rather than because he feels some sexual attraction to you now. People change a lot in forty years, and sometimes it's tough to separate the memory of what once was from the reality of now.
Make sure you're dealing with him as two adults now. Also, ensure you're honest with both him and yourself about your feelings and who you are as well as what you want in life. Take it slow and get to know him NOW. I suspect he has a much more complicated life than he is revealing and may want different things than you do. That's okay.
Don't rely on texting as the basis for a relationship, as it can never replace good old-fashioned conversation and face to face romance. See if he'll meet you casually over lunch or drinks and take it slow, getting to know him before you rush into confessions of how you feel.