To introduce another dimension -- and I hope no one is offended by this -- and with the full disclosure that I'm 72 and zeroing in on 73 ...
My experience in several community bands is that ... let me put this delicately ... the trumpet seems to get a lot more challenging to play in tune as one ages. A LOT -- just based on my observations. A lot of people in their 60s seem to be able to do it okay. But I can think of only one guy I personally know in his 70s who could pretty reliably play in tune. He was a long-time member of one of the US service (field, I think) bands, but in the past year I notice that he's moved from playing regularly in one or two organizations to subbing. All the other 70+ (and some were in their late 80s!) trumpet players I've played with just couldn't sustain reasonable intonation.
I've had similar experience with trombone players (section mates). There's a point where they just won't go near a 1st part and struggle with some of the 2nd.
I'd love to get a flugelhorn and try to play it. But based on my own experience playing high 2nd trombone and 1st trombone parts, I know I wouldn't have a prayer of doing it well at this point. And if I did, I'd expect it to degrade in just a few years.
As I've said in another thread, I don't want to be that guy: the one who can't manage to play in tune. My own recommendation for doubling at this age is not to go in the direction of one of the high brass. If you're inclined to, then definitely first try it out for your own enjoyment before taking it on the road. I may still get that flugelhorn at some point. But I doubt it would ever be leaving the house.
Gary Merrill
Wessex EEb Bass tuba (DW 3XL or 2XL)
Mack Brass Compensating Euph (DE N106, Euph J, J9 euph)
Amati Oval Euph (DE 104, Euph J, J6 euph)
1924 Buescher 3-valve Eb tuba (with std US receiver), Kelly 25
Schiller American Heritage 7B clone bass trombone (DE LB K/K10/112/14 Lexan, Brass Ark MV50R)
1947 Olds "Standard" trombone (Olds #3)