An ex colleague (& good mate) of mine is in his 60s, & has a dp of my age (early 30s). Apparently it was a bit weird meeting the 'in-laws' as they're younger than him, but otherwise they are very happy.
It probably helps that she's a quiet, 'surrendered wife' (ugh) type though tbh - I've known my friend 15 years, he's always had younger laydeez in tow (believe I was on his 'to do' list at one point...), & I suspect it's only a long term relationship because he's consciously putting his hell-raising days behind him, iyswim. But it does semm to work for them, which is the main thing...