Megfox. There are loads of topics on MN that don't involve 'chatter' about babies etc. Even mums (well parents actually - yes, we have some guys here too
) of small children want to have a natter about all sorts of other things.
And there are loads of MNers who are around your age - if not older, many of whom have adult children and even grandchildren. We...erm...middle aged people don't need a middle aged forum, we can just join in any conversation.
If you search for 'All Topics By Category', there's an A-Z list of everything. How about Adult Fiction, Adult Non-Fiction, Book Of The Month, Telly Addicts, Weather, The Wine Club, Gardening? Honestly the options are endless.
As BIWI said, hang about in _Chat for a while (it's right at the bottom of the A-Z list) and Am I Being Unreasonable (AIBU) - it can get a bit 'heated' in AIBU sometimes, but you'll get used to it. 
There's masses of grown-up fun to be had here with many, many lovely MNers - they're kind, funny, warm hearted, helpful, irreverent, sometimes smutty, sometimes 'shirty', but it's great.
Beware - it's addictive! And never take a drink of
or
while you're reading a funny thread 