Can a 17-year-old play for our club U20 or senior side?

By default, no. SARU's Regulations for Under-Aged Rugby: Adult Rugby say players younger than 18 may not play U20 or senior rugby in any position. Age is counted at 1 January of the year, so a player who turns 18 during the year counts as 17 for that whole year.

Club U20 waiver (Addendum 3, 2021): a player who turns 18 during the year may play club or community U20 rugby only, in a non-front-row position, if before any squad training the club obtains, on SA Rugby's standard templates:

1. the player's voluntary assumption of risk and indemnity;
2. parental or guardian consent and indemnity (if under 18 when applying);
3. a sports medical practitioner's rugby-specific assessment and clearance letter;
4. confirmation from an SA Rugby-accredited high performance testing centre that the player meets the reference data for the position;
5. confirmation from a World Rugby Level 2 (or equivalent provincial) coach that the player is at no more risk than eligible players;
6. sign-off by the provincial union's General Manager: Amateur Rugby (or equivalent).

The documents must be on record at the provincial union, and the player must give a copy of the sign-off to the referee before every match. Players who turn 17 or younger during the year cannot get a waiver.

Senior and elite U20 rugby: only players identified by the province or national structures as elite can apply for a separate waiver to play elite U20 or senior rugby, so an ordinary under-18 club player cannot play senior club rugby.

The club must keep documentary proof of players' ages. Costs are for the player, club or union, not SARU.