How long I have to wait to donate blood again (i can't wait long)and can I start weight training immediately?

2 months. Red blood cells take 6 to 8 weeks to replenish. There are many other components of blood that replenish sooner such as plasma. However, most donation centers do not allow repeated donation sooner than 8 week. After donation it is advised to hold off on strenuous activity for a few days. If you get lightheaded or dizzy, then rest is advised and you should see your physician for evaluation.
56 days & 3 days. You may donate blood every 56 days. You should wait at least 3 days prior to strenuous exertion / heavy lifting...Particularly at 50+ to be safe.