I dare say you could have an exciting life just about anywhere, but I do think London is really special.
I was born there. I grew up there. I raised my DC there mostly. I have lived and worked in other cities in the UK and abroad, but, to me, nothing compares to London. I've been poor there, to the point of hitch-hiking around, surprisingly successfully. Admittedly I lived in some unappealling places. I've also been more comfortably off there, which is more fun, as I imagine would be the case anywhere. I do think it's a comparatively good place to be poor as public transport is so good and less expensive than many cities, and there are so many things to do that are free. If you live there you get to find how to do more expensive things on the cheap.
I think it's a city that works for any age. There is loads to do for families, indoors and out. Obviously there is a huge variety of work. And, with excellent transport (free buses with an ordinary Bus Pass and free everything with a London Freedom Pass) and lots of places where it's quite acceptable to sit and relax, it's great for older people. I've never felt unsafe there, even though I managed to pass through Brixton when people were gathering for the Riots - nobody showed any interest in me.
I also think it has improved massively since I was little. The public transport is so much better. The air quality, although still not ideal, is much better. It's years since I've had the black snot that I used to get there. The choice of restaurants and cuisines is much better - a big uplift on just Lyons Corner House, hotels or the Cafe Royal! Swathes of dreadful housing (I've lived in some of it) have been demolished and improved, although there's always room for improvement.
I also find people there are very friendly and helpful, but you have to make the approach - they leave you alone if you don't, so you can live anonymously if you prefer. Every single time I've asked for help I've found many willing offers. It can be a bit overwhelming if several people have different ideas on, eg, the best way to get from A to B.