Specifying only a set number of months to charge a subscription is not possible yet, not with s2Member or with s2Member Pro.
Some of the gateways integrated with s2Member support that, but s2Member cannot be configured to work this way yet. For now, "Buy Now" is the only way to accomplish this (charge only for a set period of time, but in one payment).
Until this feature is implemented with s2Member, there
is a way to accomplish it with PayPal Standard. If a site owner adds a hidden input value to the Full Version of their PayPal Button Code, they can control how many times a recurring payment will be processed by PayPal.
srt (Optional) Recurring times. Number of times that subscription payments recur. Specify an integer above 1. Valid only if you specify src="1".
Reference article:
https://cms.paypal.com/us/cgi-bin/?cmd= ... 8A6HI00JQUThen make sure your Auto EOT Behavior is disabled to leave the account unchanged and he'll keep the access.
WP Admin -> s2Member -> PayPal Options -> Automatic EOT Behavior -> Enable s2Member's Auto-EOT SystemI hope that helps.