I'm 45, started this donation cycle at 44. Limit in the UK is 40-45 depending on clinic. I went to KCH, that link has all the tl;dr you could ever use on the general subject.

I thought I said this in email before ... the UK typically has ~500 people a year wanting sperm, but only ~300 donors' worth of sperm. So donate and it will be used if they can use it.

They don't notify, but I can inquire about it later and find out if it's been used. This will definitely not be for at least six months. The sperm may be kept and used up to about 10 years, I think.

My incentive for this was that I wanted more children but the loved one doesn't (having had two others before). The process is sort of laborious and long winded, and I didn't get paid. (Some reimbursement is possible, but it's strictly limited to travel expenses, and I have a monthly train ticket anyway so I didn't bother asking.) Basically it's me doing something that feels to me like I've spread my genes and is a small social good - and when I said this was my reason for donating, they said that's the usual case amongst donors (many of whom are gay men who want children but are, obviously, quite unlikely to have them in the usual sort of long term relationship with a woman).

Things different to your notes: The physical testing is of the sperm itself and a blood test, there was no physical examination. The personal background and "why are you doing this?" ethical talks were two ~1hr chats and were by far the most laborious part of the process. There is no signed contract to provide sperm. I was adopted, so only know a little about my family history (my birth mother got in touch with us a while ago and so I have a whole extra family I know something about); but what little I do know was fine. Once they're ready for donations, the main burdensome aspect is appointments and travel time; in my case, whenever I couldn't make it they had no problems rescheduling.

Under UK law, a sperm donor who goes through the HFEA-sanctioned process has no parental rights or responsibilities. However, since the interests of the hypothetical child are considered the most important thing, said child has the right to find out about the biological father at age 18, name and provided contact details. (The father has no right to contact the child.) This single thing, unfortunately, appears to have been enough to scare a lot of donors off; hence the shortage.

Other thing to note: I tried donating in 2010 and, despite proven fertility (my daughter), my sperm wasn't healthy enough to survive freezing. Then I stopped carrying a microwave transmitter right next to my testicles (i.e., I switch off my phone's radio when it's in a trouser pocket) and by a year later it was apparently much better. Did I mention they're really keen for donors, enough so they're willing to try people again?