Because he thinks you're hot.
Look, if you're hesitant, don't do it. I'm sure you're right, that he's a nice guy, but he's got kids and a divorce, and that's a lot of baggage for anybody to help someone carry no matter how nice they are. If you're not interested, tell him you're flattered, but that's as far as it goes.
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He stays in a bad relationship "for the kids". Is this a good thing?
I'm 22 and my ex was a divorced 32 year old with 2 girls. we started dating when i was 20 and he was 30. he was a really great guy, we're still friends and have tons in common we're hanging out tomorrow infact. sometimes age isn't as big of an issue ;p.
however if your childless, and still care free, then yeah that's a lot to take on with the kids and divorce.
me and my ex both had kids, he was in uni, worked, etc. it was a bit too much for the two of us. the age wasn't an issue, just the time.