I had a T-60 for many years (they were produced in 2006 - 2007), until I needed something faster and passed it onto a friend in need.
Last week he asked if he could upgrade the RAM. It was 2 GB. While it will TAKE 2 2GB SO-DIMMs, it will only recoginize and use a total of 3 GB RAM.
Is it still bullet-proof? YES! Is it capable of some serious multitasking? Not any more. I think the main thing that killed limited RAM was the change in Internet Browsers that ran the program for EACH WINDOW to prevent cross-site scripting. So, while you may see multiple tabs open, the entire program runs for each tab, gobbling up memory.
In other words, this laptop is PERFECT for your teen, which will slow down (Virtual Memory swaps) the more he multitasks - which will help keep him out of trouble on the Internet.