Most glider seat belt attachment fittings are the limiting factors
for weight in the seat. For most, the max weight is 242 Lbs or
110 Kg.

To be specific, the seal belt attachments are designed and certified to
not
fail in a 40 G deceleration with a 110 kg person.

If you weigh 120 kg (265 lb) then try to keep your crashes down to
36.7 G.

In the USA, insurance gets to be a problem in that area. If one
intentionally flies the aircraft over a certain placard/handbook limit,
and has an accident, then this becomes a way for the insurance
company to deny payments.

RO