Wow, you are awesome OP! This is a big deal for you and your daughter. I had my 3rd daughter 12 weeks ago and to be honest she was not planned, though her father and I adore her. I am 38 and was dealing with having a baby after 9 years, let alone even thinking about being a grandmother. It is not an ideal situation but I am sure with yours and your husband's support, your daughter will be a fabulous mother. An unexpected pregnancy is hard to adjust to at any age. My DP was a first time dad recently at 32. After some time your daughter's boyfriend may come round to the idea of being a dad. He is still quite young, so understandably it is a lot to deal with, hopefully he will learn to look forward to it, if not, then it is he who is missing out. My DP is a fabulous dad to our bub and and my older girls adore him too.
Hopefully things work out for your daughter, with you as her mum, she sure is lucky.