I think the problems with a large age gap between spouses tend to surface later on.
I've a couple of close friends, women in their 40s, and it has suddenly hit them that their DHs have less than 8 years to retirement and what that will actually mean in terms of finances and savings. In both cases, the couples still have fairly young children and one couple has a child with significant SEN requirements that will mean the child needs continuing support into adulthood.
With the other couple, it didn't kinda click until they were considering moving house because their home was now too small for their family and realised they couldn't get a reasonable mortgage because they were limited by the length of term.
I think you have to go into a large age gap relationship with your eyes open. A very close friend of mine is in her early 50s and her partner is in his early 70s. They've been together for 20 years, but now, financially, things are quite tough and are likely only going to get worse because he has only had his state pension for the last seven years and they are relying on her full time salary, which comes in at about the UK average. Luckily, they only pay a peppercorn rent for their flat, but if that ever changes, it's going to be very hard indeed.
All that said, my Dr is younger than me by a few years (not many at all) and I do think that was a contributing factor to our delay in starting a family, which has now had quite significant repercussions. Had DH been older, I think he would have more aware of family life sooner and been a bit more on the ball about it all.
So there's swings and roundabouts whatever, really.