There is no age limit, in fact being older than 21 likely means your going to be pushed towards the front for any companies not trying to wring out every last cent,
But realize you wont be sat down in front of a cad package designing tektronixs latest flagship without some serious experience behind you, and the ability to convey that level of intellect,
If you go for smaller businesses your more likely to be put in a seat where you get to do something sooner, learning as you go, as it will be more a culture of many hats, where as big companies will likely not let you do the role unless you can prove your fit for it at the door, as every minute your not making them a product your costing them something. if your being taught, your costing them your time and your trainers. this is a culture i am far too familiar with and why i jumped to a smaller business.
Also be aware with what titles your willing to accept, do you want to say engineer, or are you ok with a role in that field, even if you are not titled as one?, e.g. Electronic technician,
And finally, have a nice hard think if layout and design is all you want to do, imagine coming to work for the next 3 weeks doing nothing but laying out a 8 layer board, because the schematics keep being revised as the requirements changed. would this drive you mad, or would you be happy just to do that job? Accepting that you likely will have to work as part of a team, which you may not like the ideas of, or the standards you have to work to.
I'm an Instrumentation & Control Trade, with the title Instrumentation Technician, A trade course, that began repairing electronics for my company and then playing the many hats game shifted towards designing products and getting them manufactured. But being a many hats culture if i get stuck or frustrated i can hop over, do some site work, or repair some electronics, or manage a few of our web packages, giving me time to step away, clear my head and come back at it fresh, without having the stress of it being my single role in the company, or feeling like i am chained to a desk.