Male. can i do weight lifting like bench press after mastectomy? what timeframe?

3-4 months: Bench pressing put stress on the chest wall and associated muscles. If a true mastectomy with removal of part or all of the pectoralis muscles is performed, undo strain can pull the chest wall repair apart. Wait 3-4 months and perform the exercise with caution starting with small wts. and then increasing them if no excess stress on chest noted.

Yes when wound heals: after cleared by your surgeon, some times skin flaps are under tension any additional stress will disrupt the wound .