For the whole population of a country it is probably fine to assume that curve form. The first time I had my own computer was at age 7 or 8 which was already highly unusual 20 years ago. But today this is less unusual, the availability of decent gear is more common for children. On the other hand, right now many 60+ year olds don't even use internet. Those who do might be bad-ass veterans that never lost interest... ;)