encourage it: first, when I was 15 I was obsessed about a 20 yr old who i totally would have married had he reciprocated my obsession. But it wasn't until I was 17 and met my 43 yr old now fiancee that i became a Christian in the first place. my mom had tried to force me to be a christian, but it only turned me away from God. Now she rejects my relationship with him and gave me the famous ultimatum so i had to move out. It was the best thing to happy to me given my situation and not getting along with her while i lived with her. I've been happily with my fiancee for 4 years and continuing. So here's the thing, you can either be that mom (like my own) who rejects the relationship and makes herself sad and miserable everyday because she can't stand the thought if her being with an older guy, still looking at her like she's a baby with lesser intelligence and immaturity and depending on their relationship to fail , expecting it so be some sort of prodigal son story, praying to god for the relationship to end, then complaining about how she doesn't visit you that often and having division between you and your daughter.....or you can be an exemplary christian parent who follows biblical principals and ignores the physical like God does, and only look at the heart, inviting him over with her, getting to know and love him as a son, inviting him as part of the family and encouraging unity. age doesn't matter. It's just a physical material factor like money and anything else. all that doesn't count in God's eyes and you gotta ask yourself other challenging questions like what if she had gotten with someone who had got both legs blown off in war and has PTSD? or what if she gotten with a midget? non of that matters either! really it would be good to see some christian parents out there step up to the plate and respect their daughter's decision to be with an older man, although it can be emotionally challenging for most parents....but like my pastors have always said "usually what God wants us to do is the thing we feel we don't want to do". not to mention you as a parent have every right to be able to determine whether this is truly a good Christian guy or not, first start with trusting your daughters judgment because i believe she deserves that if you believe you've raised her right.