What are the most common age groupings on sign-up forms?

Under 16
16–18
18–21
21–35
35–50
50–75
Over 75

Although I have to admit I picked these numbers at random.

There is no standard. it depends on the groupings that are applicable to what you need the information for.

@marinelife The products/services he’s offering are suitable for anyone over about 16. He’s really keen on getting as much general information as he can, so I assumed something that skipped too many years per group would be too vague. On the other hand, how many choices do people want to see when registering on a site; not many, right?

He says the information itself will be used to target them specifically for particular courses/ offers from his business, something like “Send the ‘Young people’s communication workshop’ offer only to people in the under 20 age group”

@GrayTax

Under 16
16–20
20–40
40–60
Over 60

You don’t have to ask about age to get useful information about targeting them. You can ask for education level. You could ask about entertainment preferences. You can ask for many things.

Your guy should really think about whether there is some other issue that would help target people more effectively than age, and if so, figure out how to ask about that. Remember, these things are proxies for something else. As yourself what about age predicts whatever it is you are trying to predict. They ask yourself if there is a better predictor that is easier to ask about.

That’s about a thousand dollars worth of advice for free there. I could take you further, but I have paying clients waiting.