How long have you used the old-fashioned dumbbell and don’t change it, and what weight is your now dumbbell. Your strength might have improved a lot while you don’t know. In other words, you need to incentivize your muscle with more weight than before. Come and see our suggestion.
30kg is a suitable weight for mature body-builders to use. You can use this pair for bench press to stimulate pectoralis or for dumbbell curl to stimulate the biceps of your arm. The little big weight can help you both gain muscle whilst protect you from big weight injury. So, don’t hesitate!